As in all professional-class jobs, "passion" for one's work is an incredibly powerful form of coercion. If you "love" what you do, then you can guarantee that management/administration/executives will capitalize on your "love" for your work. This is as true in game development as it is in law, medicine, etc.
Among other reasons, this is why labor unions came into existence, as a way of checking the coercive power of capital. Coercion isn't simply about forcing people to work more; it's about finding ways to capitalilze on workers' own desires (for more money, promotion, recognition, or out of "passion" for the work).
The barrier to unionization is the same barrier among professionals as it is among industrial labor: the systematic demonization and dismantling of labor unions by big business (and their supporters in government).