They stated they had to replace all the servers for XI not long ago, and that the 32 bit server code was built in a way that it didn't fully take advantage of modern server tech. So they would of had to buy servers and run them way under capacity.

They now run multiple virtual operating systems on each new server simultaneously, this meant they needed to buy far fewer servers and it's cheaper to run than it ever has been before.

https://www.youtube.com/watch?v=zFqNtMJCVwY

57min