Most unions function to keep an established order where seniority matters more than capability and performance.
Besides sports unions, actors guilds, and other small examples, unions exist to provide a framework for collectivising unskilled labor into a unit of power, where individually they have none.
Even unions in industries with legitimately undifferentiated labor will have shift differentials built into their contracts.
https://amp.theguardian.com/football/blog/2023/sep/20/inter-...
What you’re doing is trying to craft a special definition of a union that excludes the most analogous unions to the one that software engineers could form and ignores the real examples of solidarity between professional class and other types of workers. See also the solidarity strikes against Tesla in Sweden. I won’t speak to your motivations in attempting to do so, but it doesn’t correspond to how labor organizing is actually practiced.
Most importantly because companies have no good way of judging skill of developers.
And also because, in most companies writing business software, good enough is good enough.
Listen, I know as SWEs, we're supposed to reject unions because we're paid so well, and listening to a lifetime of anti-union propaganda that leads to hilarious conclusions like the above. But reading some of the other threads complaining about work conditions that it sounds like a majority would like to avoid, not to mention some of the horror stories out of, eg, video game development studios, getting people to understand that, no, a union could be useful is, for some reason, an unhill battle. Wouldn't it be great if we didn't have to try and do deep work in an open office floor plan? if there were more conference rooms? If RTO wasn't a thing? If there was no deathmarch to make the upcoming release?
Because people who can compete on skill could band together and say "we're not putting up with open office floor plans".
I mean, the “on skill” part is superfluous, but, yes, it is definitionally true that a union is for workers that no longer wish primarily to compete with each other, and who realize that such competition is a race to the bottom that works against them and for the benefit of their employers.
All organized groups are rejections on some level of competition among the members in favor of cooperation for joint advantage.
I'm not saying they are a bad thing necessarily, but they don't make sense in competitive markets.