For me the main reason has been the Linux support in Steam. If they later add a Linux port, you don't have to buy it again, just go install it on Linux. Their

For me the main reason has been the Linux support in Steam. If they later add a Linux port, you don't have to buy it again, just go install it on Linux. Their work with the Proton compatibility is bringing a lot of my old Windows only games to Linux too. I'll probably continue buying exclusively from Steam for this reason.