When you are hiring at those high rates quality goes out of the window. The companies were so big and growing fast that all external leaders would hire their loyalists. The hiring quality was dropping steadily and then dropped sharply. There were some well intentioned special hiring initiatives which were in theory supposed to preserve the same quality of hires, but in private the HR leaders responsible for the initiative would send everyone a private message saying "Wink wink, this hiring is for special initiative, please please keep that in mind". The thing is if you don't have immediate customer feedback and the company is not in survival mode, empire building just takes over. I have worked at multiple of big tech comapnies and all just daily remind of "Yes Minister"