You say that, but I bet if someone offered him half a pizza he'd do it.
Different timelines. Not even a multiverse thing, it seems like everyone here is from some kind of fictional media in other people's worlds. We've got Star Wars, Harry Potter, Disney movies. There's also about a dozen different timelines from our multiverse. There's a few dozen from ours but a lot of them are X-Men, not many SHIELD agents. A lot of the Avengers are from another place. Steve is younger. Their world only started getting superheroes pretty recently and there's hardly any of them so far.
Right now, mystery cruise ship. We've hit three stops so far, Atlantis (not ours), Middle-earth and some kind of fusion fairy tale land. Before this we were based in a tiny town in Texas and every so often we get pulled somewhere else. No one's figured out much of the how or why.
Also people can come from different points in time, so, what's the last big thing that happened?