I understand the cynicism and scepticism but sometimes it’s as simple as Julian says it is, and I have no reason whatsoever to doubt him. Sometimes it’s as simple as Microsoft saying, “Hey, we like your game, can we give you a bunch of money and in return we stick your game on Xbox Game Pass on release day?”. Other than Snapshot getting a brown envelope (benefits…self explanatory), this also works for Microsoft as it gives them another title which they can add to Game Pass for very little work, other than stuffing aforementioned brown envelope.
I’d only start thinking otherwise if they were on board from the beginning, which they weren’t and neither did Snapshot need Microsoft brown envelopes to finish the game (for PC).
Added: let’s all remember that this also isn’t porting of old, i.e. PC to PS3/Xbox 360. These new consoles are closer to being PC’s than they ever were and cross platform development is nowhere near the headache it used to be.