if the truck didn't back all the way in, the smaller cars would have a problem getting out

Then they shouldn't be parked there from the start.

If there's no parking for full-size vehicles

Then, again, they shouldn't be parked there from the start. It's not a difficult concept.

Aside from the lack of care for others I think there might be two problems:

1. the local government is so carbrained this isn't illegal
2. the local government is so carbrained the fines are too low or the enforcement sucks in another way.

This car should get towed in my opinion. Sure i can walk behind it, but how about that single mom with a stroller or a veteran in a wheelchair? Sure those are stereotypes but we can't have those people deal with this shit by themselves everytime. I think you are right, just because we can pass doesn't mean we should let this be none of our business. Especially if we have a loved one who wouldn't be able to pass this car we should do something about it. Even if we don't, we shouldn't sit idly by if we can do something about it (not saying we should slash their tires though, that will probably only extend the time the problem is there).