While a dojo may have impressionable young adults who don't have the life experience to know the difference between hard motivation and abuse, those young adults are still free to leave.
Ashley, I'd say you haven't spotted what could be determined, by some at least, to be abuse, because you haven't been in the "system" long enough. Usually by the time it becomes more apparent, people are nearing or at the shodan level, and certainly around the sandan level. By that point you have people who've invested so much of their time and effort learning an "art" that the idea of freely leaving often implies - at least initially - that their practice and progress would grind to a halt.
Some people do leave after shodan level. It seems to be a big exit point in not only aikido, but other martial arts as well. And perhaps those are people who really did want to go after the achievement - the metal - the trophy.
But there are other people who are overall more passionate about the discovery and enjoyment of it all. Where shodan is just the beginning, not the end. And it's in those people that you'll find a number of ways that they find - or discover - to continue. Some are in schools and organizations, and it works fine for all involved. Others may find that stepping out of the hierarchy and discovering the resulting freedom is their path. And often that kind of decision does not come quickly or easily, and often comes only after the cognitive dissonance - created within the student by the hierarchical organization - is resolved.
Ultimately, any study and endeavor is the sole responsibility, not of any school, but of the student themselves. And the interesting stage is when the student discovers the "center" that harmoniously exists between them and the school - regardless of where the artificial lines in the sand of the perceived, current hierarchy appear to be.