[ThrowawayR2]

Unions benefit workers by giving them leverage through collective bargaining. For the US specifically, demand has been so astronomical for developers for the past couple of decades that most wouldn't have gained additional leverage from joining a union. Don't like your working conditions? Just job hop and get a pay increase as a bonus.

That calculus might change if demand for developers cools down as a long term trend but it's not going to be anytime soon.