Because now there's a finite score. Even a bad shooter is going to make around 50%. Every one he hits puts you closer to the final score instead of trying to maximize the offense/defense possessions so you can trade 3-for-2.
Trying to trade buckets 15 times in the last few minutes by fouling and forcing the clock to stop on their offensive possession makes sense. Immediately conceding a chance at two points when a set number of points beats you doesn't.
I don't disagree with you, it's just that I know how desperate people respond. A large part of what makes college basketball great is the unthinkable happening. There is always a chance. That's why I mentioned teams down four end up losing by ten. They take crazy risks that have little chances of working.