Because Lutris on Bazzite is a baked in .rpm, instead of people needing to layer it in OSTree.
Basically the same thing any normie Atomic Fedora users would normally be forced to install as an OSTree layer, from RPM Fusion.
Bazzite does this stuff out-of-the-box + flattens steam+lutris into the image.
Bluefin and Aurora users don't care about the % losses from playing games via steam/lutris flatpaks.