Because Nvidia can't write a Linux driver worth a fuck to save their lives.
I have two Zen3 PCs, a desktop with Nvidia graphics and a MiniPC which of course has AMD graphics. The MiniPC is flawless. The desktop has issues resuming from suspend — occasionally gives no graphics, switching to a VT sometimes works, sometimes restarting X will graphics working again but sometimes not, suspend with a graphics-heavy application running and come back and it's usually hung and graphics won't work correctly until a full reboot, etc.
If your use case involves Nvidia and Linux and it's not headless, you've got a bad plan.