Lot's of good reason not to. Netflix has a very precarious model. Their only revenue model is subscribers, but as they face ever growing prices for their "original" content as they bid against Amazon, Hulu, and others, and soon, maybe Apple, they are growing closer to a point where they might not be able to raise prices enough to pay for their ever more expensive content. While they have bought rights to some impressive "original" content, they are also still dependent on other entities for the majority of their catalog to let them redistribute non-original content. Apple, Amazon, Google and a growing number of others can use the their content as a loss leader. It's somewhat analogous to Spotify, although Spotify also has ad revenue, but both are competing amongst giants who have other revenue sources.
Yes, Apple is looking for content to incentivize people to sign up for Apple Music, but paying $60 billion dollars for Netflix is far from a no brainer.
BTW, you made the claim that Apple's record with content isn't as good as Netflix''s. But Apple has brought in exponentially more money from content, e.g., Apple Music and iiTunes, than Netflix likely ever will.