Regular updates are not always because of bugs but to support new hardware. Or security fixes.

If the update is only for supporting new hardware, then there is usually no benefit to the user. They already have a machine that is supported by a previous firmware version. Only in those cases where a user upgrades the hardware there might be a benefit.

Why can't the BIOS/UEFI offer some basic initialisation functionality and then the OS (Linux, Windows, ...) does a more advanced initialisation? Why does it have to be so complicated?