If instructors are unhappy with the PP program, they can actually choose to opt out. This is especially true for those who believe their courses are high-quality. If they did, students in the PP would find that all they see are junk courses, which would in turn push them to purchase the high-quality courses individually through the retail model.
However, Udemy is well aware that this isn't an issue with the PP itself, but a matter of crowd psychology. They know that only a few individuals will choose to opt out, while the vast majority of instructors will simply complain without taking any effective action