h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

The Dewey Decimal System is an interesting one, and though there are many things wrong with it, think of how many libraries still use it! Library of Congress is the obvious other choice, but still, that is not an ideal system, though it has more room to grow without having a call number that is a thousand digits long.
There are several reasons that public libraries still use Dewey. The first and foremost being that librarians as a whole HATE CHANGE. They would throw fits if someone took away their normal classification scheme. Another is that the public is very used to the system as well, and would be even more confused trying to find something if faced with the LC Classification System. But normal humans are more adaptable than librarians.
Neither system is good - both are racist and misogynistic. Both are Christian-centric and confusing. It's how one learns and what one learns in the beginning that makes the most impression and seems the least confusing. And usually that's Dewey, because most humans start in public libraries.