Only it wasn't. The Northwest Ordinance was written the way it was specifically to appease slave states. It was calibrated so that slave states would outnumber free states by three even in the worst case. Everything from the slavery question, to the question of conditions under which territories would enter the Union, was settled in a fashion meant not to anger slave states. (Except, of course, for a few questions settled for what we, today, suspect were generous sums of money. But those were things like education. ie-where and how a university would be established.)

In fact, even a review of the Congressional Record, which I had the misfortune of having to do on these very two questions for a Capstone project back in undergrad, makes that very clear. It's obviously been a very long time, and the material involved was voluminous, but I can't recall offhand any mention of the penal labor industry. The debate was dominated by appeals to interests and even feelings of slave states.