Cuz they're from birdlikes who did'nt have arms and they evolved them over time to help guide all the beef jerkys to their mouths?
All Jokes aside if i remember correctly I read that they might have used them to help them get up from laying down. I know I read that thought tiny the arms had some muscle to them and could lift like 400 pounds each.
Well, the were probably still large compare to the little dinos, but just small compare to their own giant sized bodies. I mean...
Tyrannosaurus (and its closely related genera Daspletosaurus and Tarbosaurus) had their arms shrink because at their point of evolution they no longer were necessary. Like the terror birds that preceeded them, Tyrannosaurs focused on speed, and on force bites. Arms at that point became totally useless (they were still strong, but useless for clawing or holding onto anything). It's speculated that if those animals had kept evolving, they would have been armless. Now if you think about terror birds, which are flightless birds that hunt ground dwelling animals, they focus on speed, and once again, the bite. They had totally useless, tiny 'wings'. Same goes for modern flightless birds (though they aren't specifically hunters and are mostly omnivorous). The same principle applies to other non coelurosaurian, large apex predator dinosaurs like Giganotosaurus, Mapusaurus, Carcharodontosaurus, and others. Think of chickens. Do they do anything with their wings while they feed? No! They just endlessly peck the ground, looking for scraps. These animals were probably the same. Always looking for scraps, using their overdeveloped smelling capabilities for this objective. And as for that 'getting off the ground' thing, it's still quite plausible. The arms were small, but they were strong. Still the animal would have used its powerful legs, and its tail to balance itself off the ground.
