Because then you're also taking on the administration of content delivery and payment for the same. That all takes time and money to spin up and market - which a bunch of networks have done, making their own streaming platforms. I'm willing to bet that a good number of those "second tier" direct to consumer streaming platforms aren't making as much money as the networks had hoped, while also adding a lot of administrative overhead. So they're moving back to just licensing the content to Netflix and Hulu and Amazon.