So the US is pretty demographically heterogeneous. Instead of a "we're all in this together" attitude like they have in (for example) Iceland, a lot of people here have a "us v. them" attitude. I think a lot of this is fueled by conscious or subconscious racism.
I believe this is why we have trouble passing a lot of social welfare programs, education reform, healthcare, etc. You hear a lot of complaints that boil down to "THEY will abuse the system" meaning whoever the speaker thinks is undesirable.
And that's why people like the "pay it forward in the drive-thru" style charity: the people you are helping are more likely to be just like you.
Someone in a car at a fast food place is probably well off enough to afford the car, maintenance, gas, etc.