I always wash...
you should wash them before... Hell knows where our hands have been.. However, I do agree with you, I hate it when people don't wash their hands.
For the most part it is common practice. How ever you may have times when you do not have the facilities to do so. IE: Port-a-pot, going in the woods, etc.
I guess they think that they do not have to? Maybe they want to spread disease?