There seems to be a lot of debate in the comments, that are disingenuous arguments.
I think the quality of the software is a factor for some people, but that's not the main issue here.
Steam has always publicly stated their competition is piracy. They have to be more convenient than piracy to survive. And over steams lifetime I think they've demonstrated that's their goal, yes they have DRM, but only to satisfy publishers, they've done everything they can to keep things as convenient as possible.
Epic, the company, has demonstrated their goal is money. And they've demonstrated an anti-consumer trend, the exclusivity deals are in great indicator of that. If epic became as popular as steam, they would make the experience awful, they would become the Disney of the game world.
So all of the arguments about
*launcher quality
*availability of DRM free games
*some publishers choosing to release on one platform
Are missing the mark, many people don't want to financially support a market participant who will make their lives worse in the future.
If you don't like valve, that's fine, support a different distributor who makes the ecosystem better, like GoG.