Teaching -- why do they bother?

I'm quasi grading my non-favorite class (the other section has D1 and the Russian in it, how could you not like it??) --

I have at least three students who are failing the class automatically -- by not turning in the major paper. I have a statement in my syllabus that says that if you don't turn in one of the major assignments in the class (an exam or large paper) you fail the class. It is simple... to avoid it you need to write one 5 page paper and take three exams, each worth 50 points. If you do that, then I'll calculate your grade for the course. I announce it in class several times, especially when it comes close to my cut-off for late work and it is on the syllabus.

I have at least three people who didn't turn in the paper.

These same people turned in the final take-home exam and they particpated in the presentations.

What I want to know is WHY? A coupld of them are missing enough assignments that they fail by points. Another needs 95% on their last exam for a D --

Sounds like it is time for a wake-up call for these folks. I'm REALLY glad I got tenure this semester... it could be a long summer of grade appeals for me and the super-dean.