[aahortwwy]

A major reason why engineering teams at these sorts of companies grow so large is because of how quickly the business operates and the company's rate of growth. These factors put the engineering team in a position where they're constantly having to choose the faster, easier option in the present despite the fact that it will produce a lot more work for the team in future. When the future rolls around they're still under the same constraints so they hire more people to deal with the problems caused by their past decisions while making the same kinds of decisions in the present. Rinse and repeat for several years as the company grows into a behemoth before going public.

One interesting thing to note is that as these constraints relax (business stabilizes, growth slows) the engineering teams can make better decisions in the present, clean up the decisions of the past, and reduce their overall need for people. If the company has built a money-printing machine the redundant people are then moved to new lines of business funded by the money-printer. If there's no money-printing happening, margins are super thin, and there's an incentive for the company to cut costs... where do those people go?