They initially paid a lot of money to hire the best and brightest minds, they created crazy algorithmic interviews and a lot of hoops and became known as the place where the best went.
Then it got inverted that the best go to Google so if you were at Google you were the best. Which led to people optimizing for the money.and optimizing to get into google. The problem was what was once a singal and a filter then became an objective and a goal.
Overtime the organization crew and people left due to culture changes from being a scrappy startup to being a F50 company, or retiring or just wanting something new.
The problem was the best and brightest had put together systems that couldn't be maintained by those that weren't also fantasticaly competent, after debugging is twice as hard as coding and all that, and so slowly over time the whole house of cards is rotting slowly overtime as more and more problems accumulate but the individuals left aren't competent enough to fix them or address them, and I don't just mean at the engineering level but the whole stack from engineering to upper management.
The Goths showed up sacked Rome for its wealth and treasure but can no longer keep the grain coming and the fountains running.