Except that unions play an important political role. They receive Democrat political support for votes.There’s no doubt if the government enacted laws that protected workers then there would be no need for unions yet here we are with a need for unions.
The paradigm shift occurred when Trump crossed party lines by reaching out to the angry white votes, many of whom are in union labor, and shocked the nation by winning the election.
Suddenly the union vote is no longer guaranteed, even with Democrats doing their best to show their union support, like Biden refusing to recognize the success of Tesla, a non union American company.
In my past work environment I encountered a significant number of highly paid union formen and other white workers who are Trump supporters, which to me made perfect sense even if I found it deplorable.
But your circular point is valid. Should unions be disbanded? Yes, at the same time as corporations financing political parties to loosen regulations. As I wrote before, labor rights and protections should be apolitical and under the responsibility of a non political government agency. Today's most successful companies in the US are non union. I think that speaks for itself. The battle should be to fight corporate efforts to loosen labor regulations.