Kind of a weird observation...

They do, but this is primarily a male activity. We, as males, gravitate towards things that exude power, strength and essentially, dominance. There is a psychology behind this and that is what sells.

But there are other things like Sci-Fi, figurines and flats, anime subjects, dinosaurs and a whole panoply of oddities that are not machine related. Nevertheless, they must be sought out, as they are not mainstream.

Good points, both of you! 

I think most models are armor, aircraft and autos, for a very simple reason.

Building an elephant and stomping around the house trumpeting makes your wife look at you funny!

Whereas going boom, boom, zoom zoom and vroom vroom is more fun!

They do in a limited way but there are large toy companies that produce such items.