Most students in CS are hired prior to graduation. On both sides the savings of skipping that last semester are marginal, and on the student side there's a nontrivial opportunity cost. 6 months of: studying whatever problem you want with the background you need to maybe solve it, networking, building code/ideas you own, socializing with a purpose (courting) or for fun, or, if you're smart, a bit of all 3.
There's a discrete jump in the career value of the education between not quite finishing a degree and graduating. It's not because there's some super important final semester that's worth much more than any of the previous ones. It's no doubt because it signals some quality like conscientiousness, or perhaps is just easier for an employer to evaluate the meaning of.
