Its most likely got something to do with the Disney Vault. Movies like Beauty and the Beast, the little meramid, snow white, bambi, peter pan etc are kept in the Disney Vault and released ever 5-10 yrs or so for a limited time before being put back in the vault. While their in the vault no one can broadcast them on TV and once their out of the vault they can only be shown by Disney themselves (on the disney channells). Movies like finding nemo Bednob, mary poppins etc are shown because they are never put in the vault, disney don't see them to be as valuble as the others hence these are the only ones other channels can broadcast.
Sad truth if you want to watch one of the classic disney movies you have to buy them on DVD.
I've been wanting to watch Cinderella and sleeping beauty for ever as these were the movies i remember from my childhood but cinderellas still in the vault, although sleeping beautys out so can get that.