I think it's because society likes to believe that people that do not believe or worship a higher power, are up to no good. A designated place for athiests and agnostics to feed the poor would put a large amount of doubt in that. It's a good idea though. I would support it.

Because Atheists and Agnostics have no reason to proselytize, therefore little reason to organize. Look for volunteer opportunities in your area based on things that align with your values. You're bound to meet a core group of like minded people.

There can be. Someone just needs to organize it. If you’re looking for something that doesn’t exist, find like minded people and make it happen. Go for it!

Maybe you are asking the wrong question?
The question needs to be: How are we going to create meeting places in communities where atheist and agnostics can go and do the work to make communities and the world better?

Maybe we could start here within our Community with something like "Atheist-Agnostic Chatroom" or "Atheist/Agnostic Exclusive: no talk of god in here, pls.."" Guidelines will include stern warnings and heavy penalties, even disbarred from the Agnostic.com.

You can probably check online for atheist meetups near you.

Atheists are very hard to organize as a public force, due to the prejudice against us. Most of the atheists I know, are involved in one way or another with charitable causes. It might be volunteering, public protests, or donations, but we are out there. Unfortunately, it is not known by the public.