>they've got such a nice position in the economy there's probably a bit of an "if it ain't broke don't fix it" mentality. Is that correct?I'd say your intuition is basically correct. If we use average programmer's salary of $84k[1], that places the income in the top 30%. If we extend the statistics further to include Silicon Valley salaries of $200k+, that places them in the top 5%.
I can't think of any unionization in labor history that originated with members in the top 5% of salaries. That includes unions in manufacturing, arts (film/tv), sports, transportation, etc.
Yes, NFL & MLB players make a lot today but their unions happened before the advent of TV and playing pro sports was not a highly paid endeavor. (Early MLB players had to have 2nd jobs and share hotel rooms on the road.) As a thought experiment... one might argue that if the NFL were to restart today after the invention of TV, there would not be a players union. Instead the roster of 53 football players would be 53 independent contractors. Indeed, modern players in "sports" teams like eSports are mostly independent contractors. The technology of tv magnifies individuality (Tom Brady's face also sells cars & watches for endorsement deals). Today's marketability of the individual instead of the team would make it harder to convince 50%+ of players to elect union representation. (NASCAR drivers and UFC MMA fighters had/have grumblings about union representation that have gone nowhere so far. Also, they first have to switch to from independent contractors to employees -- which is another set of hurdles.)
Some airline pilots (with seniority) are 5% salary but in the 1930s they weren't when the union formed.
So, when would 50%+[2] programmers willing want to pay union dues -- say 1.5% (SAG) or 1.4% (UAW) of their salary?!? When the economic conditions of programmers match the poor conditions of the previous successful unionization efforts. We're obviously nowhere near that situation with software devs (even ones without college degrees) earning good salaries.
Some other commenters recommend that now is the best time to unionize because the current times are good for programmers. My question to that is... has that ever happened in history?
Basically, the main driver for unionization is economic conditions instead of ideological stance. If one believes more in the the ideology rather than economics, then yes it seems realistic to think that top-5% salary earners will vote themselves into a union. Since I emphasize economic conditions, I predict they won't -- at least not within the next 10 years. If a breakthrough AI happens to make programmers a commodity equal to burger flippers, the economics stresses on the profession changes which makes unionization more realistic.
[1] https://www.google.com/search?q=average+programmer+salary
[2] https://en.wikipedia.org/wiki/Card_check