How many of Steam's competitors offered third party games? I don't have any interest in using a launcher from a publisher that only sells/launches its own games. I'd have to remember who made what, and deal with different TOS.
Battle.net is still limited to Activision-Blizzard, with a sprinkling of other Microsoft IP following the buyout. Although that might change soon?[3]
[1] https://www.ea.com/ea-pc-third-party-titles-2022
[2] https://gamesbeat.com/ubisoft-welcomes-third-party-games-on-...
[3] https://www.gamedeveloper.com/business/cd-projekt-red-and-bl...