It’s because companies have tricked them into thinking that joining unions means they wouldn’t get paid as well or would restrict their promotions. Also they had it pretty good for a long time as their jobs were in demand which gave them more negotiating power so they got paid better and had more benefits. But now that their jobs are put in danger by AI they are kinda fucked since they individually don’t have the same power anymore, power which they would have as a unionized block.