I am actually going the other direction, I used to build my own, went to laptops-only for a while but then got a mini-tower prebuilt. That one died after about 18 months so I recently ordered an even smaller Gigabyte Brix, with a 10W CPU (Celeron J4105) instead of 65W, but better I/O, and compatible with my existing RAM and storage options. Small enough to mount on the back of the new monitor I'm also getting. I have gone smaller with every desktop I built.

Basically, I now use laptops for games and the desktop for storage/office tasks. The single board desktops are quickly growing out of the RPi-type niche and look increasingly competitive with the traditional ATX platform for this role, and opting for them means that I define my system around the storage and RAM, rather than the multitude of PSU/motherboard/CPU/GPU/case combinations, which is both easier for me and eliminates most instances where components push each other out of their tolerance range. So long as I'm on the same memory and storage, I can replace everything else in the case for <$200. This is really what sold me on the idea; since my existing system fell out of warranty after one year, repair would be the cost of a new board. But if the whole system is the board, then a failure is a forced upgrade.