A big part of this that's unpopular to discuss in current culture is people actively avoiding going to a church. Whether you actually donate and believe everything that is said isn't really a factor in whether or not you can show up every week, meet other people in your community, participate in events, be there for each other at during the hard times in life, have fun activities for your kids where you can meet othe…
I've thought about this a lot, and I agree with you. I'm a pretty devout Atheist (is that the right term?), but I do recognize the social role that churches play and I wish there was some similar secular organization that could fill that role. Or course there are hobby and special interest groups, but I can't think of just a general gathering where everyone is a regular and friendly like my church was growing up.
A number of atheists have felt that, and some have even established groups modeled on the social aspects of churches without the particular theistic views (e.g., Sunday Assembly.)