Perhaps, I've formulated not exact enough. I was remembering what has been demonstrated in the famous video [1] for Athlon 1400 and 1200. Yes, the went not in flame but just in smoke. Back then the user was allowed to install a cooler direct onto the die though AMD CPU had no thermal protection (just thermal diode for emergency power-off the whole system by BIOS?).

I have no confirmation for the following but I've considered that the pre-installed and hard and risky to remove the pretty massive heatspreader plate works not only as die physical protection but also as a minimal needed buffer for heat dissipation in case of rapid cooler removal.

[1] "What happens when the CPU cooler is removed?" (Tom's Hardware Guide, 2001)

https://www.youtube.com/watch?v=y39D4529FM4

https://www.youtube.com/watch?v=UoXRHexGIok

P.S. Another rather philosophical question I have since a ventilator (not just some heatspreader) was required for the first time for CPU to operate as advertised. Can one consider that CPUs are actually factory overclocked since then? Even though not to the absolute limit, e.g. Celeron 333A (@66) up to 500 (@100) manually.