I clean up after my dogs not because I am serving them in some capacity but because they aren't going to do it themselves and:
A-) I don't want to walk in dog crap in my yard, have my lawn ruined, or have it become disgusting and attract flies since they go in one relatively small area. I would also like my yard not to stink to high heaven, and I'm sure my neighbor's appreciate that as well.
B-) in places like parks/trails/the street/other people's yards/campsites/places other people will be, it's consideration for other human beings. No one wants someone else's dog's crap in their yard, and no one wants a park visit ruined by piles of steaming dog crap. Lots of people not doing so also means the loss of access to other people's pets and that's not cool, either. (Ie: No one picks up for long enough everyone loses the right to use it because management 'ew grosses' out'.
We don't pick up after the dogs for the DOGS - the dogs don't care. We pick up for the dogs for our own sanitation, convenience, aesthetics, and respect for other people and their property.
So, I find people weird in a lot of ways. This isn't one of them.