My father works as an engineering consultant for major oil companies, and he has the same deal. He charges the companies for every hour he spends preparing for

My father works as an engineering consultant for major oil companies, and he has the same deal. He charges the companies for every hour he spends preparing for the presentation, so the actual presentation can be less than 10% of the invoiced amount. If you look at what tenure track professors do, it's the same thing. They'll spend hours working on their lecture notes that they get paid for (admittedly, most TT professors work 80 hour weeks). Not paying instructors to prepare for class only guarantees that they'll under prepare.