Why? While the rest of your comment explains why the plan failed, it seems like it should be pretty obvious why business would try to attract an increased supply. Hint: It puts downward pressure on price. Same reason they are trying again with AI.
> every other job I can think of at a similar salary level has entrance requirements'
Yes, the artificial restrictions on supply is how those careers have similar salaries. Other occupations moved to have restrictions so that they could have high salaries. Software never felt the need to do the same because the natural market propped up salaries just the same, but we'll see how long that lasts now before software practitioners panic and clammer for restrictions to prop salaries back up like the others. AI does actually seem to be making inroads where "learn to code" failed.
Granted, like as suggested at the top of this, the upper class of software engineers who have the necessary reputation and prestige to drive software towards being a licensed profession are not feeling the same pinch that the middle class is feeling, so that is going to make it hard to see restrictions come to fruition even now. When the upper class of software engineers start becoming afraid of shrinking incomes, that's when software engineering will start needing a license.