I would also add the fact that games people buy for XBO can be transferred and upgraded later on when they buy a XSX, so the buyer's certainly mind much less buying into a dying console due to this. And it binds them already to the Microsoft platform for the next gen even before it's out, so win-win for both of them.
I hadn't really thought of that. I was just thinking the people who are buying an Xbox One right now wouldn't be buying an Xbox Series X until a few years down the line. Plus knowing all first-party games will be coming to the Xbox Series X AND Xbox One for one to two years into the next generation has to help.