And then claim they don't like Epic because "exclusivity is bad", but work to make everything Steam exclusive.

Literally nobody is arguing for games to be Steam exclusive. Nobody benefits from a Steam exclusive either.

What people want is to have every game on every store (with, at most, first-party titles excused), so that the stores can actually compete to be the best on the actual service they provide. They don't want games to be on Steam, they want games to be on Steam and Epic and everywhere else.

The difference is that, unlike Epic, Steam is not in the way of that happening. Steam doesn't make contracts with developers/publishers preventing them from selling their games on other stores. Every game that is exclusive to Steam is only exclusive because the dev/publisher choose not to make it available anywhere else, of their own volition. Which is still bad, but it's not Steam's fault, as they are not the ones preventing that from happening.