I agree - they look nothing like the characters they're based on. I find little appeal in them.
That being said, I could understand why there's an appeal for others. For one thing, it's cute. For another, it's less about their resemblance to the original model and more about the buyer's attachment to the franchise the Funko is based on. I might find a Spider-Man FunkoPop a little too goofy for my taste, but given a choice, maybe a discount, I'd still collect it because it's Spidey, my favorite superhero of all time. Likewise with Buffy Funkos and Buffy fans. There's an attachment there.
And of course you also have people who just loves collecting these things as a hobby. I collect movie blurays myself (or at least I tried to; they're darn expensive). And with cute adorable Funkos, it makes even more sense to start a cute collection like that, figurines you could keep around to adorn your home. And I think, superhero FunkoPop is probably the most appropriate FunkoPop since comic book fans are already collectors in their own right. Even if the action figures they collect are usually more accurate to the source material, I doubt these fans could pass up the chance to collect Funkos of their favorite comic book characters, much like me and Spidey.