The idea that you’re suggesting is called union busting. It only works in USA and very few sectors in Europe where sector agreements are not mandatory by law.

I’d argue that it also doesn’t work in USA, since the companies end up spending more money on avoiding an agreement than what they’d save on salaries. They also waste a lot of time and resources on the individual bargaining, which provides no value for neither the company or the employee.

If the employers pay people more to not join a union, the union might even say: “Mission achieved without a fight. See ya’ll next time inflation catches up.”