Why can't there just be a simple D-Bus interface for pulling the 'currently playing ___ game' info (such from Steam, Lutris, whatever)? Or some other vendor-neutral API or minimal protocol for the same? Or perhaps some cross-vendor standard for sending multiplayer session invites?

Plenty of these seem like trivial ideas, and I understand there's probably many differing ways to implement such, but to my knowledge there's not a single project or standard within this field, from what I'm aware of.

I'm asking solely for technical reasons, I'm not asking about ideological explanations (since many of the answers for that are self-evident).