Yeah, the problem is, someone has to start the union. It takes work. You have to get the whole workforce to vote on it. A lot of software engineers believe (or believed) that they were too smart and professional to need a union. And of course, if management gets wind of it while you are working on setting up the vote, they may do all kinds of trickery, legal or illegal, to block it.

It is possible. But it's quite uncommon in this industry in the US.

And given the current administration, it is hard to trust you'd get fair enforcement of labor laws if the company did illegal things to block unionization.