I think you’re misunderstanding the author. The sentence after the one you quoted is

> Most of these companies have solid internship programs, and almost all E3 (entry-level) positions are offered to returning interns.

The author is saying that getting an entry-level position without an internship is very difficult at these companies and so if you want to work at one, applying as a senior engineer is a much easier route.

FWIW, I work at one of those companies and have found senior roles and promotions to actually be pretty biased toward longtime employees