Why does the BIOS on motherboards "fly off"?

Very often, the situation "the computer did not turn on" is "treated" by flashing the bios. Here are a couple of the latest motherboards:

• We remove (solder out) the BIOS
• We read it with the programmer
• Download all versions of the bios from the website of the manufacturer of this board and this revision of the motherboard.
• We see that the chip dump does not match any version of the manufacturer's BIOS.
• Upload the most recent dump-voila-the computer again it works!

The crux of the question is this: why is a chip that essentially once when turned on gives a couple of megabytes of data (i.e. works in read-only mode) can damage its contents?

Another question: this is the second GIGABYTE board with the so-called DUAL-BIOS. So - the first chip (signed on the board as M_BIOS) damaged its contents, and the second-no (checked by the programmer). But the chip on the board couldn't check the checksum and didn't switch to the second one. Then why the whole system?