Oh, comfort is a big thing. I don't deny that. I'm questioning if that counts as evidence that they might not enjoy other games if they overcame that barrier. I've had good luck getting groups to play other games. Presenting one shots or short runs so that there's not much opportunity cost seems to work well. That might be the groups I've encountered, it might not. I will say that, until the last few years, all of the games we tried had pretty strong traditional roles for players and GMs. A few blurred the lines a bit, but the structure remained. Still, I haven't had much trouble getting my current group to play Blades -- they love it. We are, however, currently playing 5e because we like that game, too. I'm excited to try running a Scum and Villainy game soon, which I know I'll have little trouble pitching and will have to actually be selective in players, but that's because I know a lot of Firefly fans and I'm pitching a game in that vein. I hope to get back to 7Sea 1st ed sometime, though, as I think I can make that game really sing by moving towards a 'play to see what happens' mode rather than the GM determined games that always seems to wilt a bit.
I run a lot of different game engines too. One of the advantages of being the GM is I can say "I'm running X; who wants to play?" Most players seem to be down for most game systems I'd consider. There are a few players that won't play specific games that rub them the wrong way. Ars Magica has a couple of players that really don't want to deal with downtime/lab work, for example.
Next time I need a recharge, I'll be running a 1-2 session of BitD. I'd really prefer to play, but there are no nibbles. The person in my circles who would've most likely been willing to run it is now a former GM :-{