Publishers had a choice, and they overwhelmingly chose to host their sites on infrastructure that was too slow. That's why the AMP project exists, to take choices like that away from publishers, because they consistently make the wrong choices when you give them one.
It is the implementation they chose, and it does have speed benefits. But, an edge cache that allows the end user more control, their own domain, an no hijacking header is possible, and would provide a notable speed benefit. If there were a choice between the two, publishers would likely pick the latter.