It is perfectly possible that a given company performance can be reached by different paths, some better for employees, some worse.
In fact, I think that even seems like a very plausible hypothesis, given that treating your employees worse can have advantages (reduction in costs and headcount) and disadvantages (less motived and potentially productive employees, worse retention, difficulties attracting people) for the employer, so those two may roughly cancel out under a whole lot of different conditions.
So for the employer there may be no benefit (but also not really a downside) to treating employees better, but add to the mix this strong cultural idea in US business circles that unions are the worst and you get this taboo against unions and no market pressure to change that.
Obviously this is a quite horrific situation to be in because we get worse outcomes for employees and unchanged outcomes for employers. So no one benefits and most people have worse outcomes. Bad all around.