Sony, Paramount, Anna Pura, Lionsgate, to some extent MGM, Entertainment One, Canal (outside of France), and a lot of major TV companies (BBC Worldwide, Endemol Shine, All3, etc etc).
There are plenty of companies selling TV, the problem is that there libraries are now in a bidding war between local broadcasters, Netflix, Amazon and some of the other services like HBO Max and Peacock. Apple is going to have to spend a lot of money (five to ten times what they've spent on Apple TV so far) if they want to win those battles. And they're a bit late to the party for some popular shows.
Hell, why license content when they could probably just buy all of MGM, LOL. MGM is basically a rights holder/licensor at this point anyway. It basically doesn't exist as an independent studio anymore. They don't even own their own golden age library.