[Kalzazz]

At least for my part, I tend to find

'What we have convenient books for' strongly influences what sort of games I will run

I used to run a lot of DnD 3.0, oh look, Star Wars d20 exists? Okay, I will run DnD 3.0 Dungeons and Dragons and Jedis

I also ran quite a bit of WEG d6 Star Wars . . . . when d6 Adventure with the Very Cool Magic System, and d6 Fantasy and d6 Fantasy critters came out, I started to run Space Fantasy with X-Wings, Magic, and Dragons

So if GURPS Vehicles (or GURPS Toaster Pastries or whatever) came out, I might be inclined to buy it and run games using it

I find Spaceships terribly confusing and problematic to use, so now when I run GURPS Space Fantasy it tends to be 'ships? What ships? Ships don't exist', back when I ran d6 Space Fantasy there were ships everywhere because I liked and understood d6 Star Wars ship stuff

By the same token, GURPS has lots of Really Awesome Fantasy Stuff, such as the DF line, Low Tech, Martial Arts, Magic, Thaumatology and stuff. I love running straight up Fantasy games in GURPS. I hardly ever ran straight up Fantasy games in d6 because well, there really wasn't much in the way of d6 Fantasy material out there, I always ran Space Fantasy because there were a zillion variants of blasters and X-Wings and droids oh my ready to go