I would think knowledge work is really compatible with unionization, as it has less "fungible" employees.

If one assembly line shift goes on strike at GM, they can switch in another crew, or hire scabs and get pretty close to back to normal.

If your software dev team goes out, any replacements don't have 200 years of experience on exactly where the bodies are buried in the specific design and architecture. You will suffer ramp-up problems. A strike threat is way bigger, especially if it cuts into keep-the-lights-on stuff like SRE and operations too.