I assume people do not want to run an OS that has "testing" or "unstable" in its name.
If you don't need the latest packages, Debian is the way to go but if you do need the latest packages, you are much better off with a distro that is primarily made for that.
The first beta had issues with crashing on Proton but it seems like they figured out the reason.
Also, there is a second beta upcoming so you can test it before release: https://store.steampowered.com/news/app/2246340/view/547849766230294535