We're hitting a ceiling based upon how many hours a single human can work without dropping dead from sleep deprivation, when you talk about 90 hours a week that means living at the office, over 90 hours a week and you're looking at only 90 minutes of rest per night 7 days a week.
We blew past the natural limit many many years ago, except the limit was artificially raised by the normalization of performance enhancing drugs (namely tea, coffee, etc.)