I don’t think common sense suggests that at all. It’s like saying that the US armed forces requires soldiers with many specialized skillsets (which is true) so clearly it should recruit to every individual role and post separately.
A large company may have a handful of actually-very-special-role positions open for every hundred generic "our tech stack is this and isn’t going to change" developer roles.
The armed forces have a service commitment of several years (if I read this correctly, US Army is 8 years). People will sometimes change jobs within months.
They have the time to train someone into a role and typically don't have to worry about going to work for a competitor after they get out of AIT or A school.
While there's nothing wrong with those companies paying such, it drastically changes the incentives for the regular employee. Going to work in Big Tech can be like winning the lottery (in the dot com boom, I had about 6 million on paper... that I didn't sell before the crash).
That there is drastically different industries with correspondingly different levels of compensation has incentivized the person who can change jobs to move from a $60k job to a $120k job to a $250k job to do so.
A large company may have a handful of actually-very-special-role positions open for every hundred generic "our tech stack is this and isn’t going to change" developer roles.