I have been DMing long enough to know that committed, responsible players are essential to a successful game. DMing is also very hard work, and requires lots of extra prep time in addition to time spent in game. I provide a quality service that is in high demand. A good DM is hard to find. I am a good DM and deserve to be paid for my work. By asking players to pay, it also ensures commitment and personal investment on the part of all players.
A typical campaign takes at least 2 hours outside of game time, often more. Ergo, I spend a minimum of 5-6 hours a week working on a game. You get what you pay for. LOL