Good point, many teachers would not find many jobs in industry. I had a BSEE and was able to transition into and out of teaching. And in engineering I was asked to teacch in addition to my regular duties. I know math teachers can make the transition if they teach the upper high school grades. So could the physics and chemistry teachers. But they are not looking for humanities teachers in most of industry. Of course individual circumstances are always more important than generalizations. Some teachers are so good that industry would want them regardless of their teaching subject or level.
I've known teachers who have left the field and made fortunes, not in industry, but in small highly specialized businesses. The only reason to go into teaching is because you have a burning desire to be a teacher. The money stinks, the hours stink, and the working environment is horrific.