Why didn't it occur to someone without occurring to someone first?

Because the idea that something this obvious occurred to the CTO first is very, very unlikely. What is more probable was that leadership ignored people who disagreed until the CTO convinced himself it was a good idea and went ahead with it.

People within Meta have been campaigning for this for _years_; even people as high up as John Carmack were pushing for open bootloaders on deprecated hardware (and he achieved that on the Go headset, but not as a general policy)