You're Still Gaming on a Xbox 360
One of the biggest reasons to upgrade to the Xbox One is that you are still on the Xbox 360 or PS3 for your gaming system.
Developers are no longer making the best versions of their games for these systems and in some cases aren't making new versions for them at all.
If you want to play the latest sports games like Madden 19 and FIFA 19, upgrade to the Xbox One. You also need to upgrade for most first person shooters like Call of Duty: Black Ops 4, open world adventure games like Red Dead Redemption 2 and any other must have AAA titles.
This is going to be a bigger issue in 2019, and ultimately this is the year you need to upgrade if you are serious about games.