Unlimited retakes would be an enormous amount of work for professors/TAs/teachers.

Optional homework is often a disaster. At best, students would do it right before an exam and the goal of education is not to just pass exams. They’d probably still get a lower score than if they did the homework when they were supposed to.

What I think is better is to have a due date, but just make the maximum 10% each day it is late. So after 2 days, the highest score you could receive would be 80%.

I liked that system because it gave some flexibility with deadlines while still encouraging you to turn things in on time.