The big upside of the trades is that after working for journeyman wages for a while, learning the job, and establishing a reputation, it becomes possible to own your own business, either by founding or buying out a retiring boomer, of which there are many. At that point your earning potential skyrockets into the millions.
The problem with this is the same as assuming that every developer is earning a GAFAM salary. It just isn't applicable to the average employee in the given profession. I'm also extremely skeptical that yearly profit potential is in the millions for trade businesses except in extremely rare cases.
It’s pretty easy to search business broker websites for $1 million and up EBITDA businesses. I can’t answer your question about prevalence from that since I don’t know on average what percentage are for sale.
I do know though that it’s pretty common for the seller to write the note financing the deal, especially when the buyer is a soon to be former employee. So financing is often within reach.
Another example is trucking. Plenty of trucking businesses were built by a lone operator rolling profits into more trucks and hiring drivers. Given the intense competition for CDL drivers today though it wouldn’t be my first pick.
If you start selling millions in contracts, then are really doing trades any more? You are a business manager and you need business management skills. Many people go into trades specifically to avoid that kind of life, they could have gotten a business degree instead if that is what they wanted.