Firmware will typically configure the SPI controller such that flash can't be written directly from the OS, both as a self-protection mechanism (there's been ma

Firmware will typically configure the SPI controller such that flash can't be written directly from the OS, both as a self-protection mechanism (there's been malware in the past that deliberately bricked boards by overwriting the firmware) and as a security boundary (if you can modify flash directly, you can replace the set of keys trusted by secure boot).