the main difference is that MMA has always been a business, it was born a business, unlike football (soccer) , basket ball, tennis, who all have a long history, they all have regional, national, international organisations, profit never were the goal ,even now when it come to soccer most clubs aren't profitable whereas nobody start an MMA promotion to not make money
so even with an union , more promotions, you can't expect mma to ever be like those other sports, it will always be an sport/business hybrid