They didn't. The Beatles lost control of Northern Songs (their music publishing company) in 1969, after their publisher (Dick James) and his partner sold their interest in the company to ATV. ATV bought enough other shares (Northern Songs was a public company, traded on the London Stock Exchange) to become the majority shareholders. John Lennon and Paul McCartney "cashed out" at that point, selling their stock to ATV also. (George Harrison and Ringo Starr kept their shares, totaling about 1.8% ownership of the company. Each had already started their own publishing companies, independent of Northern Songs.)

Northern Songs went up for sale in 1985. McCartney and Jackson were friends and collaborators at that point, and McCartney encouraged Jackson to invest in music publishing (which he had done in the 1970s, and prospered), never expecting Jackson to outbid him for Northern Songs. Afterwards, McCartney pointed out that his and Lennon's writer's royalties had never been increased (they were young and naive when they signed the initial contracts, and weren't paid what they easily could have been), and asked for an increase. When Jackson turned him down, it was the end of their friendship.