Hey, I'm not into vore. xD

But I know exactly what you mean, I see it everywhere too.

it probably has a lot to do with the mythology/stories around dragons, like they steal/eat the princess and depending on the story would do the same to passers by or a knight coming to save said princess. snakes/predator type animals/some other mythological creatures have a similar reputation where they come up as "man eaters", so when people think of vore, they are more likely than not to be what comes to mind first. also i am sure the size part comes into play a bit as well, because many dragons are big enough to actually eat someone whole (same for snakes as some do get big enough to eat people)

I'm more into puffs than vore...