My wife and I have taught in public schools, private schools, public universities, and private universities for 35 years. We've both taught as adjuncts and both also been "tenured" (what we call a "continuing contract" in some states).
First, the longer you stay as a professor at a university, the further behind you get...this is well documented. If you want a raise, you probably have to seek a job at another school and move (we've done that a couple times). Professors and higher paid teachers used to make a middle class salary, but in recent years they've been falling behind. Many state university systems have paid few real raises in almost 20 years.
For example, here in Florida an engineer, desirable business degrees, and almost any STEM major might get $80,000 as a starting salary if they were a good student and had a good track record. That's what energy companies, government contractors, international marketing, etc. pay for skilled and educated students. I can name students who got those salaries in the last few years.
Next, both of us have made double or triple the $'s simply by going outside the education system. With 5 degrees, my wife makes about the same teaching as a new undergraduate major in one of the desired majors. Whenever we get behind, we have to stop teaching or work nights, holidays, and weekends on contracts outside of our schools to make ends meet. Every year we get full-time offers from private firms at salaries higher than we get teaching. If you have a marketable skill, you can usually find someone to pay you!
There are a few professors who are way overpaid, and usually the really high salaries are "professors" who are administrators making crazy salaries ($200,000-$400,000 in Florida). That skews the reported averages. There are also some adjuncts and visiting professors who are underpaid and trying to move into a full-time job. In most public universities and public schools, tenure only assures "due process" if you're fired, and plenty of folks with tenure are non-renewed every year. In Florida, there are 2-3 thousand contracts non-renewed every year and many are "continuing contracts". Tenure just tries to make it difficult to fire folks on a whim without a legal fight.
It is true that adjuncts are treated badly and underpaid. No one tracks how many eventually get a full-time job, but many do it they are doing a good job. It's not necessarily true that professors make great salaries.
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