These companies become victims of their own successes and eventually become hollow money machines that are preyed upon by professional executives. The culture dies and all the good people leave except a small cadre of highly paid early employees who have worked on core services for decades.
Google's problems are so pervasive and famous because they don't care. Why fix hiring? That requires effort and time for a questionable payoff. Why fix promotions? Same problem. Why fix customer service? That's just a cost. Why enforce stable APIs that are well documented for cloud services? Not my problem. At the end of the day, a small core of people will keep ads going and everyone else will decorate their resumes for their next jobs.