What do you think? Do you think of world building as largely a GM responsibility? Do you think of the "game" as a whole as a shared responsibility? Do linear games versus sandboxes versus railroads/rollercoasters versus free for alls fit in?
All of the above; and also none of the above. I think finding the right mix of players for a group is the real challenge RPGs face. I know some players and GMs that need nothing more than a shopkeeper, mayor info-dump, and a neon sign saying dungeon this way

. Neither GM or players in this instance have much of an expectation. Others, of course, put a lot of thought and creativity into their world building and want players to explore it. Issues arise when you got a mixed bag, and in my experience you always have a mixed bag.
My first step is get on the same page as a group. I usually start with one shots so we can get to know each other. Find out who is reliable, who likes what play style, etc.. Next step is to settle on a consensus about setting, theme, system, etc... Off to the races from there.
I have not had any luck on homebrewing a setting and having any takers. Like, at all. So, I dont bother doing it anymore. I work with existing primarily in Third Imperium for Traveller and Golarion for Pathfinder. I find the players enjoy the wealth of info available, and dont seem to mind if I bend them a little and get creative. I think adventure paths have become popular because of how much footwork they can provide and offer for groups. Adventure modules, setting material, players guides etc.. Also an entire internets worth of shared experiences for both players and GMs.
I do think the GM has a large responsibility in the system they run, campaign they choose, and in which setting. As a player, I have respect for that and do my best to be engaged and enthusiastic. If I cant muster it, I will respectfully bow out. With the internets now I can be more choosey than ever. Thats not a knock on anybody else, because as I said, there really is no general idea of how this responsibility should be shared, if at all.