Why are there seven different cat registry associations in North America instead of just one? That is comparable to asking why there are hundreds of Christian denominations instead of just one. Simply put: members can’t agree on everything.
The different cat associations mostly disagree on which breeds are registered and which standards should be used in judging the breeds. For example, the Cat Fanciers’ Association recognizes a certain number of breeds, while the American Cat Association recognizes a different number, and both believe they have good reasons for including or excluding a particular breed.