This is the main problem. I buy NUCs because I know I am going to get a machine that works and if there's anything wrong with the BIOS they will ship an update, and that update will be installable without Microsoft Windows. If I am left to a marketplace without Intel's excellent BIOS, I am going to be very sad.
Assuming I'm able to run without any obvious bugs, crashes, I don't generally run BIOS updates. That said, I can understand with a more general motherboard that may swap to a newer CPU, or other peripherals.