Deeper Xbox integration, probably. Microsoft knows the writing is on the wall that Xbox Party Chat usage is way down and a lot of it has been replaced by gamers with Discord.

They know it so well the new Xbox Wireless Headset essentially has a "Discord feature" though obviously not named or marketed directly as that. (It supports dual pairing with a bluetooth phone for "phone calls over game audio", but everyone I know got the message between lines that it supports Discord chat, and were talking about the headset precisely because of that feature.)