It seems that wedding photographers keep the copyright so that they can reproduce them for self-promotion and advertising, which totally makes sense.

Also, if you think the cost is unreasonable, I completely disagree. Photography is a very expensive vocation, and the wedding season is very short. There is little room for error, and the photos have an enormous emotional significance. The event day (or days) is incredibly long, and cataloging and processing images can be an enormous time suck afterward. I get that some people may not be interested in wedding photos, but that doesn't mean the photographers are overpriced for the work they do.