Hundreds of years ago Masters wouldn't charge tuition fees to students, and they would only take on students who were committed to working hard and sticking with karate long term.
A Sensei became like a member of that karate-ka's family.
With rising costs of keeping a dojo, equipment, insurance, etc. dojos have had to become much more commercial in order to stay open. In my opinion, some have taken it too far.
You will see dojos out there that charge huge amounts of money, make you sign a contract saying you'll stay there for a certain amount of time, expensive "belt test" fees, and any other number of money making strategies.
In our dojo we charge enough to cover our costs as well as some compensation to each Sensei, but no Sensei in our dojo is making their living exclusively from teaching karate.