That's just lazy
Agreed, there is no question it is lazy. And please don't get me wrong, I don't condone the practice. I am just pointing out there are times in which this 'opportunity' presents itself and it's not really the fault of the professor.
... misses the whole point of getting a proper education
From experience I know that many can receive top marks on resubmitted work. You are either already at a very high standard, and thus it is arguable if the effort of writing another extremely similar paper (which could be spent elsewhere) would be worth the educational benefit, or standards are not high enough.
at least a bit...
Problem is, you probably need a substantially different paper to avoid plagiarism of your own work, not just a bit different.
I suppose that is possible. If you're a scene girl.
Now that would be a sight to see. A scene girl concerned with privacy.
The only perfect science is hind-sight.