Lutris exists and works pretty well. It's kind of mind boggling to me that gog doesn't double down and support linux better. They have always catered to a niche of gamers, it seems like linux would be a good fit to target. But no, steam supports linux better.
That said, I think the problem is neither of GoG's niches are growth categories. Game development since the mid to late 2000s has been pretty stagnant. You can usually expect a game produced at that time to still work on modern computers. So the pool of old games GoG can pull from is limited. Eventually, a given customer will have bought all of the old games they want, and they don't need to return to GoG.
With lutris/minigalaxy I've been digging into my GoG collection again. I've been having fun finishing some old B and C tier adventure games and playing around with some of the old strategy games etc, but I'm surprised at how many classic titles I was excited to buy again when they were first rereleased have stopped interesting me.
They saw this years ago and pivoted to focus on the DRM aspect of their store. Clearly, there is a limit to how much of a draw this is. The number of new releases has skyrocketed in recent years, and things like streaming tv have worked to devalue each individual piece of content. When facing the choice between price or drm in this kind of market, most customers are going to choose price. In many years, at which time you might start to consider whether a game is still playable, the market will be showering you with a new hot title that you would rather buy than replay something you finished and forgot years ago.
Storefronts like epic and steam are working with the market. Even things like itch have their own niche that aligns with growth forces. GoG is pretty much going against the grain here. If they didn't have to show infinite growth as companies must do these days, they probably would be OK for a while. I feel shrinking their offerings to focus on DRM as a value add... won't make an impact.