I'm sure there are some who overcharge and are greedy. But I don't think you can really call them all greedy for charging whatever the going rate is. Especially when you consider that many of them charge on a sliding scale based on the client's ability to pay. I was between jobs for a while and low on funds, and my T lowered the fee by half during that time. If he wanted more money he'd have let me reduce sessions instead of paying less for them.

I agree that teachers should be paid more but fact is, how hard you work at a job isn't the only thing that determines how much you get paid.