The barrier to entry in the trades isn't the difficulty of the work. If you trained 1000 programmers for six months, a good number of them would be competent, but none of them would be able to get licensed. Every single one of them would need to work as an apprentice to a licensed plumber as part of the licensing requirements.

On the flip side, all you need to do to get a job programming is an internet connection and the desire to learn it. Anyone can teach themselves and if you can code enough BS on a whiteboard, somebody will hire you.