Like which jobs? Amazon, McDonalds, Walmart all are non-union. Major union professions are nurses, teachers, plumbers, steel workers, automotive workers, none of which are exactly low paid
I think a prerequisite for union to be successful is that it's members have leverage by withholding their collective labor, otherwise how to they negotiate?
Collective bargaining is literally the whole point of a union (and essentially forms the definition of a union).