I think it's worth adding that Steam's (more recent) refund policy is also a big deal. Even if you don't need it, knowing that it's there can influence buying decisions because it feels more like you can "try before you buy" (although this actually involves paying before you get to try and then putting yourself in a situation where Steam could refuse to give you your money back).
After using Steam almost exclusively for years, picking up a Nintendo Switch was jarring because there's pretty much no way to walk back from a purchase even if you have only played it for a few seconds (or just downloaded it). This also goes with games perpetually sitting at AAA release day price points, release dates often being unclear or promoted more than the actual release and sales affecting your wishlist being undercommunicated in comparison to Steam.
Steam simply lures you back in by sending you that e-mail that the game you wishlisted five years ago is currently on sale at a 90% discount.