They can't due to the shortcomings of the hardware (why develop a hardened os to the grossly insecure hardware) or the vendor (no/slow updates, etc).

Anyone is free to fork, add the desired hardware support and flash.

(that's aside of some Moto flagships in 2027)

Those Razr phone updates need to start landing sooner ....

More like OEMs need to take security more seriously and add in the capable hardware and commit to firmware updates long term.