It's relevant to nearly everyone who would be interested in the title of the article, though.

how? if profession A gets more demand and pay, does it matter if profession B gets more or less? Is it that damn important if A makes more than B or if B makes more than A?

It's relevant for software engineers who read the title and consider going into data science instead.

Except most software engineers aren't qualified to go into data science.

The appropriate knowledge can be acquired if you put in effort. This information is useful for those deciding whether the effort is worth it.

The appropriate knowledge can be acquired in anything if you put in the effort.

What exactly are the qualifications? I would have thought a serious, sustained study of statistics--starting with a strong base knowledge of the mathematics of probability and building from there. But based on the resumes I've seen that doesn't seem to be the common opinion.

I would argue you are correct and those without that knowledge will find themselves in over their head quickly without that knowledge.

I'm assuming most people who are interested in the title are interested as part of the research one does to decide in what direction they ought to advance their career.

If I'm choosing to train up for job A or job B, I mean, money certainly isn't the only consideration, but it's certainly a very important consideration.

It matters when profession A and profession B are as related as data science / data engineering / software engineering.

I'm not arguing that there's no distinction between the fields, just that people who excel in one can usually do a passable job working in the others. Or rather, you have to have passable skills in the other fields to excel at your chosen field.