Or they're ashamed they've invested so much in a franchise based on toys and desperately want validation for the years of emotional and financial effort they've put towards it. I'll just settle for the toys, thanks.
It can be done in a mature and darker toned thoughtful way. Look at Airbender. (The show.) Its got powerful kids out to save the magical world yada yada, yet it touches on everything from the war's impact on both sides, dysfunctional royal families going to the extremes, meditation, spiritual life truths, corrupt or blind governments, brainwashing, revenge, self-redemption,characters developing and maturing. While TF does not need all of that, as its not the kinda franchise it can still be thoughtful without pushing to an r rating, can still be mature and darker themed without copious amounts of blood, gore and TnA, *Ahem Bayheim.* I'd like to see it take a socio-political twist, the decepticons rising up to overthrow a corrupt government, a slave rebellion, warriors gone out of control for power over themselves that it goes to extremes and they try and control everything but.
The robot deaths were pretty brutal in the Bay movies and they were PG-13. Robots got ripped in half & rust dissolved. There is absolutely no reason to make it R. Like cartoons, violence towards robots just isn't viewed as that bad. Things that seem to get movies an R rating - A lot of swearing. In particular the F bomb - Nudity - of people - Gore -blood & guts - especially of people None of those have any place in a Transformers film.
And "great" is subjective depending on the context. I mean, it's already been pointed out that trying to up the rating to a hard R isn't going to solve anything. It isn't the violence that's the issue with the Transformers bay films, or at least not the major ones given more often than not said violence is cited as being the only parts of a film most people find tolerable. The problem is with the handling of the characters. What's the single most cited problematic scene in AoE? It isn't any instance of robot-on-anything violence, it's that dumbass Romeo and Juliet scene that the production team even admitted was not in the finalized script but largely made up on the spot because it amused them for some reason. So little care was given to making the films feel like a Transformers film, in so far as the bay films go, that as I often say, if you replaced the robots with ten foot tall predator aliens that turn invisible to 'disguise' themselves, the plot could be largely identical and nothing important would change beyond superficial details. Compare that to something like Detective Pikachu - not the greatest film ever but it is undeniably all about the pokemon from start to finish and it is dead-on with its adherence to retaining or otherwise explicitly referencing terms and mechanics within the franchise's world and lore. And one of its biggest plot twists is entirely telegraphed beforehand if you know what to pay attention to and are familiar with a specific pokemon's trait, but it does such a good job of misdirection (despite the bad guy being blatantly obvious the first time he appears on screen, but this is a kids film in the end) that it caught me completely off guard when the reveal dropped. Spoiler: The single best part of Detective Pikachu That fucking Ditto, my god. You are straight up told the bad guy has a Ditto, who is seen turning into some kind of assistant guy helping the wheelchair bound bad guy, but said Ditto is strangely absent for the rest of the film...or is it? Nope, turns out it was the mute bodyguard and the sunglasses wearing son when Mewtwo is recaptured, and then in the 'final confrontation', the fake son morphs back into the bodyguard who takes the glasses off...and it has those goddamn signature beady eyes that are a dead giveaway it's a Ditto. The resulting beady eyes on a human face is absolutely, gloriously surreal. Or, to use a more unofficial version, Dragonball Z Abridged Popo. In canon, he's this relatively useless genie guy who lives in the sky with Kame and is essentially around to just help the main fighters become ever stronger or otherwise provide plot-driving devices. In Abridged, he's basically cthulu and makes absolutely no attempt to hide his contempt of everybody except Kame and everybody rightfully fears him...except Kame (they just get high on pot together) and the Great Dragon (Lord Popo is in fact the dragon's master). The reason I bring this all up is to show that smart and appealing characters or gimmicks don't need the ultraviolence an R rating can allow - the talent behind the scripts and the direction simply needs to be better when it comes to telling a story and keeping it related to what the story is supposed to be about.
Eh, I think it's as much that there's fans who don't have children and don't buy the toys so it's easier for them to forget that toys are the main reason for the franchise. How about because it would be nice to be able to take my niece to a Transformers movie? Because I sure as fuck weren't going to take her to any of the Bay movies and if the future movies are anything like them, I'm not going to be taking my nephew to see them either.
I'd like to see a Starscream film - which would ultimately actually become a Megatron film - as a terrible character that does horrible things to an even more terrible character, resulting in one or the other dead (or at least deactivated) by the end of the film and the audience more than relived when the Autobots do finally show up to save the day. But not R-rated. PG-13 robot violence is just fine.
I want a movie where the Decepticons really question Megatron's leadership and he has to prove himself worthy. A movie that follows a small group of cons on a jorney.
And why would they suddenly question his leadership if he's already the leader? And what does this have to do with them going on a journey-
An R rating adds nothing of value that the series needs. It's usually just a crutch for faux-edgy "mature" nonsense or stuff that you can still cover in a PG-13 production if you're careful/tactful about how you handle it. If anything, the kind of stuff that usually gets talked about with "gritty and mature" stories that warrant their R rating is more like fake maturity designed to appeal to teenagers and the like. Buckets of blood, characters swearing like sailors, shameless fanservicey nudity. None of those is mature or a sign of better storytelling on their own. Game of Thrones, for example, was 'mature' because of the scope, depth, and unflinching nature of its storytelling, not because characters visited brothels or guys got their heads cut off with fountains of blood everywhere, or because they all cursed like 21st century internet denizens in spite of it being the fantasy middle ages. Those things were added likely because they'll appeal to the audience that thinks they're a sign of maturity and make them watch a show they'd otherwise dismiss as "silly lord of the rings nonsense" (only with more swearing in that description) Would I like to see a more "mature" transformers movie that handles the great war with a bit more depth? Absolutely. But it absolutely doesn't need to be R-Rated. That's never been a part of this franchise and it shouldn't ever need to be.
Wait, are you saying that they would want to make an R-rated Transformers movie because they think the movies are bad? Gotta admit, I'm not seeing the logic there.