This isn’t a monopoly issue. Other launchers exist. Most of the games on Steam are available on these other launcher, yet people still prefer Steam.
I can only speak for myself, but I prefer Steam because it’s more customizable so I can set it to open to my library first instead of a rotating ad banner, the storefront ads are not intrusive and can be easily ignored, and steams remote play is something that no other launcher offers.
In fact, I am not sure what the other launchers offer that they excel at over Steam.