Google will hire loads of young / inexperienced people at non-senior, let them work for 8-10 years (exceeding level expectations but not getting to senior level

Google will hire loads of young / inexperienced people at non-senior, let them work for 8-10 years (exceeding level expectations but not getting to senior level), and then let them wash out to a competitor or startup. But they won't hire someone with 15-20 years of experience as non-senior, and let them do the same. Because of demonstrated trajectory and the belief that a company only needs leaders and future leaders (see also: why Google has so much trouble polishing maintaining products, polish and maintenance requires non-senior-level elbow grease) Yes, is because if uncertainty, but it has a disparate impact on older/experienced people. It's not explicit ageism no, but of courses committees arnet explicitly racist and sexist either, yet Google has no problem admiting there is an implicit problem there.