So, there is certainly a culture of martial artists who really do try to make a living out of it. We get glossy magazines from them and their ilk at our dojo all the time. It's very interesting to look at, but it's easy to see why a lot of sensei's would shy away from that culture.
There is also a lot of greed that masqueredes as self-help of various varieties. Again, something I can see a sensei wanting to stay far away from.
A lot of sensei's have a full work and home schedule that they are as committed to as they are to AiKiDo. I was actually 'brought up' in AiKiDo on the idea that the art (and the way) are properly part of a full life and should not take over your life.
Yoga is kind of funny, though, isn't it. I'm never quite sure how they manage to maintain such a aura of selfless devotion to the art at the same time the prices are so high. One thought I have had is that the particular segment that yoga originally appealed to in the united states was one that had a fair amount of disposable income and valued things in proportion to their cost. Perhaps the original AiKiDo audience was poorer and/or more frugal. Another thought is that AiKiDo is necessarily a community activity, where most advanced students of yoga do most of their yoga on their own at home. AiKiDo would get pretty expensive if I had to pay $10 per class instead of paying by the month. I honestly wouldn't be able to afford it.