...you'd be surprised by how many students do quit/drop out just because of one class, even when they're only one or two classes away from graduating.

Finally, universities measure (1) the time it takes for students to graduate and (2) the completion/graduation rate for all students who begin. Professors (really colleges and programs within a university) are actually under pressure to push students along and get them out the door. University higher-ups would most likely rather have a student pass on the first try than collect additional fees/tuition at the cost of making them stay longer or have the risk of not finishing.