I'm sure this is at least partly tied-in to their ongoing, illegal efforts to crush labor organizing at their plants. https://www.reuters.com/article/us-tesla-nlrb/worker-testifi...
How many tech workers would like their terms of employment, including compensation, to be decided by negotiations between a union and a company?
So far, the difference I have noticed between union and non-union areas is this: in the heavily unionized locales, all work done is very expensive, but it is also mostly done correctly; in the lightly unionized locales, work is inexpensive, but is slipshod, and without any express or implied warranty. Both take at least twice as long as you think should be necessary, but the union guys will at least show up and pretend to work, while the non-union guys will just ghost.
I want to be the guy that shows up and (eventually) does it right, while three other guys stand around and watch. I'd rather not be the guy that cannot meaningfully engage with the work, because the pay is peanuts, and I could get fired just for sneezing wrong. I (and my ancestors) have a deep-rooted desire to be able to dig in my heels and give someone an earful (or page-full, as it were) whenever they are about to do something stupid and involve me in it. I don't feel like "at will" employment gives me that option. If I speak truth to power, I can get fired.