... but they have exactly the same business model, and people genuinely promote valve as if they want it to be a monopoly. (though I am aware that it's not one now- first-party launchers are universally reviled by gamers).
Valve allow you to install whatever game store you want on the Steam Deck. They win custom by making a better experience than everyone else, Apple win because they have formed an environment where you have no other option.
If Apple wanted the same business model, they would allow alternative storefronts, they wouldn't block updates if they decided they didn't like you anymore, and they wouldn't block you from even replacing the OS on the device you bought if you wanted to.
In fact, I'm not entirely sure apart from running stores that they are the same thing at all.
Steam was not appreciated when it launched. It made a foothold as a requirement for HL2. Valve has done a good job making relatively painless over the last 20 years, but it was originally reviled.
It's riddled with adverts because it's the only way to get revenue out of such a terrible system.