Union culture is as antagonistic in France as in the US (for the same reasons that corporations are antagonistic) and it not only has multiple GOA4 metro systems running right now across the country[0], Paris is actually converting existing lines to full automation.

All of Germany (which has a much more cooperative union culture) has two GOA4 lines both in Nuremberg, meanwhile Copenhagen Metro (in highly unionised Denmark) was created fully automated back in 2002.

I see no evidence that unions have anything to do with it.

[0] quite literally: Lille, Toulouse, Lyon, Rennes, Paris

Unions in the US are annoyingly different: most (at least those that I'm even passingly familiar with) seem to have one major goal: keeping the status quo (with regular pay and benefits increases for its members, of course). They generally do not go for "hey, we're going to eliminate your jobs, but we'll compensate you in such a way that you'll continue to be gainfully employed elsewhere".

Often that topic does not even come up because companies are not firing people to begin with like they do in the US. They just transition into a new role (for instance they could become light rail drivers in the same network where automation is not yet achievable).