[cortesoft]

It might not brick the hardware, but it can get it to a state that makes it seem bricked to a non-expert user.

I think the fear would be that non-expert users would try to flash their custom firmware, run into issues, then try to get warranty relief claiming there is a hardware problem.

There would be no easy way for Prusa to tell whether the boot issue is actually a hardware problem covered by the warranty or a firmware issue caused by bad firmware being flashed.

They don't want to sign themselves up for having to assist users recovering from flashing their firmware.