1. Just because we have not thought of something more abstract does not mean category theory is the "ultimate" abstraction that cannot be surpassed. You would have said the same thing about sets before category theory was invented. 100% guaranteed there will be another, more abstract paradigm when the need arises.
2. Just because one thing captures something fundamental about computation does not mean it captures everything fundamental about computation, nor does it mean nothing else can capture fundamental aspects of computation (disjoint from what may or may not be captured by category theory). For example, category theory does a terrible job representing the mathematical subfield of complexity theory, despite it being entirely about computation. For that matter, "how abstract" is not always comparable, and the intellectual dick measuring of what is the most abstract is counterproductive. Even basic questions in particle physics have no known model in mathematics that doesn't break under gentle prodding, so is particle physics more abstract than mathematics?
3. Haskell does a lousy job representing the majority of ideas that make category theory useful to mathematicians. For example, universal properties are neglected Haskell, and at best they're implicit. Nobody actually thinks about the math when they're writing Haskell programs, they just think about Haskell types and programs, which makes the "techniques and patterns" of Haskell programming just as arbitrary as the conventions in random Javascript libraries. It's just that there are fewer names for the same thing because fewer people write serious programs in Haskell.