All of the fires I've heard about 3d printing involved sketchy power supplies in some of the printers or DIY builds out there. Thermal runaway protection is really easy code to write and very common in firmware and the thermal design of the heated parts makes it hard to get there.

Not saying fires don't happen that way but let's say it's a failure mode that is a challenge to achieve intentionally much less accidentally.

Thermal runaway protection does not help in certain failure modes.

Failed FET for instance. They tend to fail "on". Unless you have a highside FET shutting off the power (and that may fail too).

On my printer I have software watchdogs but I also have an entire "dumb" (no MCU) circuit that will shut off a large relay that goes to my heaters if any of it's failsafes are triggered. I have a smoke detector, secondary thermistors, etc.

There are a bit more things in the way of thermal fuses and heaters that are less likely to runaway on the newer commercial printers but I still think people need to take the risk more serious.

I have been building printers and printing since 2011 and I still prefer to not have my printer in my house where the family sleeps, even with the failsafes. It lives out in the shop with plenty of room around/above it in case of a fire.