Kind of a dumb question, you'd think this would be easy!
Buuut, I've been thinking about it lately. Mostly because people for some reason find my taste in macro smuttery baffling, and I've had to struggle with explaining myself. I don't think it's always a nice, easy answer, and I'm not really looking to explain away all the weirdness in my head with just one thing. There are lots of kinks that I've added on over the years, of course, and there's lots of angles to take just about anything in macro. It's a delightfully diverse fetish. I know there was a poll about what kinks we like, but in a way I think stuff like that doesn't really describe a whole lot of the true motivations.
Anyway, for me it's mostly about causing fear. No matter what else is going on, that seems to be something that is constantly in the fantasies I create. Gentle fantasies, cruel fantasies, it doesn't matter. Whether I'm a giant dragon little guys fear and I'm trying to get them to trust me, or I'm a giant dragon teaching little guys to fear me because I'll stomp on them, the one thing that's the same is the little guys quaking in their boots. Now, I guess this is different from being directly attracted to bigness, because just the image of size juxtaposition doesn't do it for me. Dragon bigger than planet, building the size of my toe, that's not really something that can get me going. It's also distinct from enjoying causing pain, because that doesn't really have to be present either. I thought of this because I recently played a demon dragon who was the same size as a human who summoned me (the idea being to get big later) and even at the same size I was turned on by simply being menacing. Meanwhile, an RP where it was mostly descriptions of me being larger than buildings wasn't really doing much for me.
Maybe also you could say some of it is just plain interaction, plot, dialogue, and situation. I really like talking, probably another thing stemming from just liking the emotional and fear side of it on the whole more than the physical side.
Anyway. That's weird me.