Category theory gives us a nice, high-level set of conceptual tools to try to understand and generalize over things that are hard to connect otherwise. Some people find that useful directly, other people just enjoy it for its own sake, or even for aesthetic reasons. (I think all three are totally reasonable!)

At the same time, it's actually rather more accessible than most other areas of pure math—at least at the level that people talk about it online. Basic category theory can be hard to learn because it's so abstract but, unlike almost any other are of math from the 20th century onwards, it has almost no hard prerequisites. You can reasonably learn about categories, functors, natural transformations and so on without needing a graduate degree's worth of math courses first. You might not understand the most common examples mathematicians use to illustrate category theory ideas—but it's such a general framework that it isn't hard to find alternate examples from computer science or physics or whatever else you already know. In fact, I expect most of the articles that get talked about here do exactly that: illustrate category theory ideas with CS/programming examples that folks on HN find relevant and accessible.