The large companies don't need tens of thousands of system architects. They need tens of thousands of coders who can do what they're told on small parts of a system without fussing too much about the bigger picture. I think that's what OP is referring to—leetcode filters for young developers who don't need to understand all the reasons why they're doing what they're doing.
Every job has random overhead and your productivity is boosted quite a lot by already being familiar with some random bullshit problem like "don't configure your test environment this way or you'll run out of file handles after a day or two." Hiring more experienced people means fewer delays due to issues like that, even for boring "code-monkey" work.
