Actually, McCartney didn't sell the songs to Michael Jackson. Dick James owned 40% of Northern Songs in the 1960s. McCartney and Lennon held 20% each, while 20% went to "general public" shares. By 1969, James had bought enough public shares so that he owned 51% of the rights. He immediately sold to Sir Lew Grade, who snatched up the remaining public shares. Outgunned, Lennon & McCartney sold their NS shares in exchange for ATV stock.
Fast forward to the early '80s. Grade puts Northern Songs up for sale for $20 million. Paul rings Yoko, says they can split it 50-50 at $10 million each. Yoko says they can get a better price. Meanwhile, Michael Jackson is flush with "Thriller" cash and buys the whole lot for just under $50 million.
Who the heck is Dick James?