[tech_ken]

Two answers:

* In the US there's a narrative that unions add layers to bureaucracy to a process that should (from an IMO limited "pro free market" position) efficiently settle on an optimal solution all by itself. Many people just by default accept this argument, and to be entirely fair US unions definitely got complacent in the last few decades.

* Many HN commenters are affluent tech workers or entrepeneurs, and some are bosses or capital owners themselves. People in this first group kind of "won" the economy, and in the second group actively benefit from workers negotiating 1-on-1. Group (1) has a tendency to not relate well or understand the position of the typical union constituency, Group (2) has financial motivation to push back against it.