Of course it can (and should) be done by multiple people, but there is an essentially unlimited supply of postdocs and graduate students from China and India who are willing to work long hours. A graduate student salary is peanuts for a US citizen compared to industry, not so for someone from a third-world country. This isn't hyperbole - more than half of the graduate students at my University were not born in the US. Graduate students 3-4 years into their PhD face tremendous pressure not to quit, and you usually make the decision to go into graduate school very early in your career.