Games

Off the top of my head, the biggest one I can think of that had potential was Rumbleverse, which was an epic exclusive and got shut down. That one had a lot of potential just lacked visibility. just they didn't get the player base.

But doing a quick google search also gave me quite a few more, such as Gigantic, which was a third-person hero shooter that used its own exclusive launcher along with the Windows Store.

There's the Darwin Project, which launched as an Xbox Game Pass and did eventually go to Steam. However, by the time it hit Steam, the damage was done. They had lost all momentum.

There is Rocket Arena, which was an Origin Epics game title that eventually went free to play and then closed down later.

There was quite a few MMO-style live service games, but those have tentative life spans anyway, So I don't think that it would be fully fair to list those.

There was Knockout City, which was exclusive to Origin and consoles and also had a lot of streamer support, and did eventually come to Steam(albeit mostly for their cdn system as stated by one of the devs of it)

Those are just a handful of games from a Google search, the reoccurring trait across all of them which was they were decent games that people enjoyed playing. They just lacked the user base. And by the time they made it to Steam(if they made it to Steam), it was already too late and they had already lost momentum.

It's likely that if those games had just been released day one on Steam that they would have had the momentum required to continue going. But instead they intentionally excluded the Steam user base usually due to some form of exclusivity deal.