One reason is Valve has put a fuckton of effort into linux support. So for linux users, buying a game on Steam means it’s probably going to work right out of the box. Buying from Epic, it’s a crapshoot.
For example, I spent hours trying to get Red Dead Redemption 2 that I had bought from Epic to work. Never did, something with rockstar launcher compatibility. Gave up and bought it again on Steam, worked the first time I hit play.
The same exact reply was posted twice from the same account and once from a different account with less punctuation. So I assumed they posted once and it didn’t look like it worked (but did), they tried again and it didn’t look like it worked (but did) so they logged out and back in to try again, except it logged into and posted from a different account.
¯\_ (ツ)_/¯ I’ve done it when my connection is being crappy.
IMO if it’s exclusive to one store, sailing the seas is morally just.