As for the actual publishing business, an important reason for owning such a catalog is to have some steady income from the publishing rights. For example, very simply put, MJ made money every time a Beatles song was played on the radio. Having a steady source of income like this gives a certain financial security and allows for more creative freedom, because you don’t have to worry so much about making money. It’s also an investment in the future, kind of like the luxury version of a retirement pension.
So, to break the bank to achieve all that, only to give a huge chunk of it away because you’re such a good-hearted guy and dear “friend” would be absolutely stupid.
Besides, I’m also absolutely sure that, had Paul ever been in serious financial trouble, MJ would have helped him out. But taking a multi-million dollar financial loss just to make a rich man even richer? What’s the point?