I think that poster is referring to STEM as a whole. Software engineering is a small subset of STEM, and I'd argue that it is, surprisingly, both the most accessible and the most lucrative.
I mean software. Professional sports is also accessible and lucrative in the same way. Most white-collar professions secure their gravy trains through guild membership, insider knowledge, and personal relationships. Software, however, gets more competitive throughout a career, not less, and most people don't understand how obsessed they must be to keep up. I like that about it, and I didn't make it as an athlete, so it suits me, but most people that come into this profession would rather retire into management than keep up their coding skills for more than a few years.