And you can't just assume because they have a big vehicle they can afford it or the insurance or the gas.

Their reasoning might have been like this:

1. I am broke because I am paying way too much for gas.

2. Either eat or pay the insurance bill, choose eat.

3. So stressed that i don't pay attention and hit other car.

4. Worried I will loose everything if I stop, their car is on the other side of the road and they can't get back in it in time.

5. I bet I can get away and they won't know who I am.

This is all hypothetical, but there could be many reason why a person would make a bad decision. Throw on top of that, are you sure the other driver was a legal US citizen or resident and had a valid driver's lisence, and was not worried about being deported?