Difference in business school pay across developed countries
Many universities are not funded by tuition by students. Funding from the government is not rare.
Did you remember to take into account such issues as whether the society offers reasonable healthcare for everyone, kindergarten and school for children, reasonable holidays, unemployment benefits, rights for employees, etc.? Adjusting for these might not always be in favour of USA. This also makes it very difficult to compare wages across countries.
That said, USA is a very rich country with some very rich universities that can afford to pay well.