The demand isn't strong enough. Heaps of people want to hear tapes of presidents so they are released, transcribed and published. Not that many people want to hear Tony Ducks in the Jaguar or even Castellano is his kitchen. But when it's a famous mobster, the demand is stronger so they get released:
https://www.amazon.com/Gotti-Tapes-Sammy-Bull-Gravano-ebook/dp/B0083L10J8I don't think anyone's refusing to release these tapes, it's just that the public isn't demanding to hear them and no one would make any money publishing them.
