They have an enormous back catalogue of classic albums which they do not bother to remaster or rerelease.
Sony Legacy does a great job of getting people to buy deluxe editions of albums they already own - by adding unreleased live albums, hard-to-find b-sides and other goodies to the old albums. Collectors and fans love them and buy them at premium prices.
The Warner back catalogue is so poorly managed that people will pay up to a hundred bucks in the aftermarket for an unremastered, muddy-sounding 1990 CD release from the Warners catalogue.
Does anyone at Warner's stop and think: "Hey, if there are hundreds of people bidding top dollar on an auction site that pays me nothing for a poorly mastered 18 year old CD of an album I control, why don't I just pay a few grand to remaster it and release a deluxe edition at 19.99 a pop?"
Sony is cleaning up - Warners couldn't be bothered.
Warner in milking that trend for big dollars. $30-40 for a single CD on Rhino Handmade:
Mailorder only, no stores or distributors to worry about. They get all of the money and be aware they may charge you sales tax even if you are not in california.