I feel like it should drop on Xbox first because one it’s already there and two and this is just the story part it’s basically a copy a paste
Everyone is a self-taught programmer these days..
No, it is not just 'basically a copy and paste''. Despite the game literally being the same, it needs to be recoded and made compatible with the Xbox One architecture, which isn't as simple as upgrading hardware on PCs and playing the same game right after.
We're also talking about Reachs codes integrating with MCCs code and they have to make sure they put Reach in, without it breaking the rest of the collection.
It is as far from as simple as everyone wishes it to be.