Students and Turning in Assignments

So, just today, I have had more than 5 students try to turn in work that was due over 3 weeks ago, mostly because their grades are in the toilet.

Why is it that with 2 classes left, students suddenly become concerned with their grades?
Why is it that when they actually have a chance to do something about their grades, they do not, but are willing to go an extra kilometer when there is almost nothing that can be done?

These are days that I don't like being a teacher.