In math classes, where concepts constantly build on one another, traditional policies hold students to schedules that keep them learning with the class.
Assuming all students learn content at the same rate is dangerous. There may be fundamental math skills that take one student longer to learn than another. That may mean multiple attempts at demonstrating those skills.
If I were to disallow retakes, even the intrinsically motivated student who struggles with fundamentals loses out on mastering the concept. I lose out on knowing that student is struggling. Retakes allow me to more fully assess a student's progress toward mastery, incrementally working on correcting errors and gaps in understanding.
By promoting pacing over learning, we are doing our students a disservice.