I think Boeing developers might be part of their engineers union.

Tech companies tend not to unionize, because most developers don't see net gain to be had from unionizing. Most unions end up serving the interest of the union instead of the company, and enact things like seniority based pay and promotion. There's just too much incentive to cater towards interest of mediocre employees in a union model.

Another big factor in software development is that the jobs are comfortable and pay very well. So lots of people would happily apply to the job. IIRC, it's something like a 40:1 ratio of applicants to offers at big tech companies.