Why aren't the customers going to Epic Game Store? It's the PC, after all. It's explicitly not a walled garden
The Epic Game Store is just kind of mid. The app feels spammy, the game selection is less, and it doesn't really offer anything over the existing options beyond the monthly free game gimmick. If they want customers to head there it needs to be better, not just good enough.
EGS has yet to reach the feaure parity of Steam from 15 years ago.
Who knows? Presumably because Steam hasn't done anything to drive them off, they've generally been satisfied with the service, and the titles they want are available. At least that would be my guess based on my personal experience but I assume Valve has a much better grasp of their audience than I do.
I go to EGS once a week or so just to see which free game is on offer, and the experience is only barely tolerable.
If you're giving away free games and can barely manage to attract people to your storefront, you might be doing something wrong.
In their defense I suppose, most other competitors weren't much better. I don't think anyone misses Origin, and you'd have to pay me to spend any amount of time on Ubisoft's storefront. Only GOG comes close, and they earn a lot of good will in other ways.