A worldwide shortage of gaming video cards. I've been thinking about building a new box for a couple of YEARS now, waiting on the prices to come down. I don't have any hope of that for at least another year.
My current "build" is an Athlon64 with a 760. Surprisingly, it plays a lot of games just fine, but there's really no point in putting a 760 in anything like a Ryzen. ;-)