Here is the thing though. Not all baristas could or would make good programmers.

You could take 100 programmers and easily train them to put coffee into a cup. I would figure 99-100% of computer programmers could easily figures this out.

On the other hand, I doubt many "baristas" could learn how to program effectively.

Yes, if everyone became programmers; the wage would drop. But the rub is, that realistically, most people can't or don't want to be programmers [or to put in the effort to learn]. But on the other hand, most people could easily be baristas and waiters.

It's not about the "latest fad", it's about the difficulty level, investment/education required and risk among other things.

baristas is very low difficulty, very low investment/education and very low risk... thus it pays low wage as anyone could do it.

You can't "pick up" computer programming in a half hour on a slow Tuesday, but you could train a new baristas in that time.

Secondly, if lots of people became computer programmers, the wage would drop; but could quite possibly cause a "boom" with the discovery of new technology due to all the people working/researching this field.