Earlier quoted context omitted.
It's a thought, but ceteris paribus, software engineers seem to have a particular scorn for unions beyond the calculus of economics. In other words, there is a personality/sub-cultural disdain for unions. I see it as an extension of a distaste for bureaucracy or perhaps, social structures in general, but I'm open to other perspectives.
I think a lot of people (especially tech employees and HN commenters) have this idea from the 80s and 90s of what a union must be, like they are all necessarily just like a Teachers' Union. Usually bad stereotypes like "Unions rank members by tenure and reward only the old timers!" and "Unions make it so only union members can plug a cord into an electrical outlet!" and "Unions only negotiate for salary, never things…
Take the NYTimes tech worker union, for example (previous HN discussion: https://news.ycombinator.com/item?id=41504026). It really only has 2 objectives on its platform: indefinite remote work, and "pay equity". Notably, their objective is for pay equity regardless of different representation across different jobs. So not even "equal pay for equal work" but rather "equal pay for different work".