Gregory's Server@brouhaha @uncanny_kate plenty of reasons. Most importantly, work efficiency is not static. Say in 8 hours of work per day you get 8 units of work done. Then it's pretty safe to assume that working 10 hours would not yield 10 units, but less. And at some point, additional work hours might cause negative units BC. of errors due to overworking/attrition, ...
@ang_mo_uncle @uncanny_kate It's been shown that the value of additional work beyond 8 hours goes negative very quickly. If you do it rarely, the value might actually be nine or more, but when done frequently...