My (conspiracy?) theory is that payrolls are padded by design. Suppose Google gets out of the unprofitable aspects of their business and cuts back drastically. You can probably get rid of 50% of people while keeping 90% of revenue. You could say that its not forward looking as these "other bets" could pay off in the medium to long term, but this has been going on for a while and it's pretty obvious by now that other bets are almost always bad, definitely not worth the investment.
Even if they are, a place like Google doesn't have the right structure to compete in these markets. Things aren't dire. I remember a portion of Chaos Monkeys where the author describes Google+ as an existential threat to Facebook, so he drives to the Google parking lot on a weekend and finds no one there. Obviously Google+ wasn't a serious enough concern to Google that would require weekend hours so the author concluded (correctly) that its not the existential threat that Facebook thought it was.
So what would efficiency look like? Well, Google's gross profit margins are 55+% and their net profit margin is around 25%. It's hard to find those margins in other competitive industries. So what would their margin be if they cut expenses by 50%? They would have uncomfortably high margins that look bad to regulators. Similarly they would have a ton of excess cash that they would have to pay out in dividends or stock buybacks (also politically unpopular). To add to that, managers would reign over a smaller domain.
You see the same behavior at utilties companies where they're allowed to charge cost + markup. They have no incentive to bring costs down if it just means they have to charge less. Obviously there are no price controls affecting Google, but if their margins shot up to 100%, it wouldn't look good.
So a place like Google allows for inefficiencies and bloated payrole because it keeps everyone happy (other than shareholders) and it keeps them off the radar of more strict regulation.
https://www.macrotrends.net/stocks/charts/GOOG/alphabet/prof...