Because lets be honest, getting a great GPA in school is not difficult. I am sure if you guys put in the same effort your LSAT as for your school work, on a consistent basis, almost everyone here would be 3.9+
Um, I'm not sure whether to fire up the ROFLcopter, sputter in disbelief, or envy the living shit out of what must have been your undergrad experience.
Aside from my wholehearted disagreement with such a sweeping generalization of a statement, you do pose a good question. Of course, the people who had less-than-stellar ugrad GPAs (whether through lack of effort or matriculation in a school or program that doesn't toss out A's just for showing up and doing the work) are definitely more inclined to bust their asses on the LSAT. A lot of us only firmly decide to pursue law school after graduation, at which point our LSAT scores are the only significant variable we can actually do something to improve. And, of course, busting one's ass for a few months is much more manageable than doing the same for four solid years, as you suggested we should have done. Comparing the effort and approach of studying for the LSAT to that of studying in college is beyond apples-and-oranges. It's like apples-and-goddamn Klingons. (I'm not even going to touch on the glaringly obvious issue of people who had to work during college or faced any of life's other myriad complications that would have made all-day, every-day studying impracticable.)
So, short answer: yes, people with low(er) GPAs probably do tend to pull out all the stops on the LSAT for the simple fact that they must, if a top law school is what they're after. Asking what "drove them to care", and thereby implying that they gave zero fucks about anything before the LSAT, is both utterly inane and the height of douchebaggery. (I'm sure that wasn't your intention, but still. I didn't intend to sprain my ankle this morning, but I'm sitting here in pain all the same.)
Hope that helps answer your question.