I could make a LOT more money as a Clinical Psychologist in private practice. However, I enjoy teaching WAY more. Hence, I'm leaving the counseling field to teach at a small liberal arts college where teaching takes precedence over research. Its a pay cut. I could easily be making 1.5x-2x my salary in private practice, but how much I make isn't the driving force in how I make the decision. In fact, I just got forwarded a job opportunity last week that would pay twice what I will make in this professor position. But, I've spent some time working in private practice and I just didn't enjoy it. I was effective, both by empirical and anecdotal evidence, but I didn't look forward to going to work in the morning. On the other hand, I have worked both as an adjunct lecturer and an instructor as a graduate assistant and LOVED teaching in both settings.
Thus, just because one teaches doesn't mean that they couldn't make money practicing their trade. It MIGHT be true, it could be true for some, but it isn't necessarily true for all. Not everyone makes their career decisions based on what will bring them the most cash. As long as I have enough to provide for my family and have a little fun while I do it, I want to look forward to going to work in the morning.