Why? I like Transformers. There's as much play value for the dollars spent as in any other toyline in my opinion...except for maybe Legos.
In some cases (movieverse, mostly) I was buying every onscreen character that came out...until I realize how much I disliked Rampage and Mixmaster (not very fun to me)...so I passed on a few. Didn't bother with the offscreen characters until I saw how cool Bludgeon, Mindwipe, and Brawn were.
I tend to buy most Primes, Soundwaves, Bumblebees, Starscreams, and Grimlocks that I encounter. Sure, they get reissued and reinvented to hell and back, but I like the different takes on the iconic characters.
I've taken to army building a little...so I have a small platoon of Ejectors, Ransacks, and Ravages.
If I find a well-priced G1 I don't already have I'll add it (Seacon set).

 

For me it is the character and toy. I try not to by non fiction characters and crappy toys.

 

If it looks cool,it's bought.

 

Because they appeal to me in some way, shape, or form.

 

i like the way they look and im somewhat obsessed which makes me even buy the toys i dont think are great but for some reason still manage to pick them up

 

Why do I buy the figures I buy?

Obvious answer is that I'm a Transformers fanatic, so of course I'm going to buy the toys.

To be more specific, I collect a wide range of toy lines... the majority of my toys are from the Movie-verse lines, with Classics/Henkei/Universe/Generations and Animated following closely behind. I have also collected G1 Reissues, Alternators, and Cybertron and hope to collect more toys from those lines... as soon as I get caught up on all the Movie, CHUG, and Animated figures that I want.

I don't buy all the repaints/retools unless they look awesome (the ROTF Armorhide repaint of 07 Movie Landmine is one example) or they are necessary (the Classics Seekers for instance). And for the most part, I buy from the lines that matter the most to me... since I'm big on G1, Movie-verse, Animated, and Cybertron, I'm going to primarily focus on those toy lines (or toys that are inspired by those series/movies).

 

I pick up a TF because I'm a fan of the character, like the looks of the toy or both.

 

Interesting answers. Oh, and I've noticed some posts saying things like "Well, cause I'm a Transformers fan." I'm not asking why you like transformers toys, I'm asking why you like specific transformers toys.

Just thought I should clear that up.

 

Hmmm, most of the time I try and get all the movie toys, to complete it all, unless it's a pointless toy (Tuner Mudflap)

 

Why do I buy transformers? Well, I was introduced to TFs through the Beast Era, and afterwards had a majority of the Armada and RID lines. I really enjoy the possibility and the injinuity of the figures. I now collect CHUG figures.

What determines a purchase for me is either I like the character or the toy looks awesome. At first I was sort of a completionist, but after some, questionable purchases (I'm looking at you Universe Smokescreen) I'm trying to buy more because I want the figure and less because I feel I need to buy it.