Students are also people. If we're managing a software project, a single deadline at the end is sure to suffer from delays. It's better to split things into shorter deliverables with more frequent feedback.
Few students do optional assignments unfortunately. Other tasks that are directly worth a gradetend to take priority (e.g. studying for another class that has an exam this week).
1. Class attendance is frequently optional, but students still attend.
2. I had a prof. that didn't require homework be done. He would give out "practice fun" and would gladly sit down, give feedback and 1:1 time to those who completed it, or tried. He also pointed out that it was rare to pass the exams for students who didn't do "practice fun". Most people did the work.
It leads me to believe - from my own experience too - that students generally aren't stupid, and will gladly do the work if there is a point. Plenty of homework is pure busywork though, even at the college level.
