From my practice there are simple measures to avoid failures.
Do not place these boards in the closed case, setup the fan to cool the bottom layer of PCB.
Do not allow the local overheat of any component like DC/DC or external power connector.
Turn on the overtemperature shutdown in the bitstream, and control the temperature in the mining software. It is easy.
Then the FPGA board will work for years.
I agree. But there will always be people looking to squeeze out every drop of hash.
So if you set 75(c) they would set 85 (c) hoping for more hash and faster roi