1) Much easier to implement and maintain for small to medium architectures. However, war stories I've heard is that it starts to become a hassle for large clustering architectures.
2) Because it's a traditional message broker, the input and output ends, which I was responsible for, were much simpler to write because I didn't have to worry about replays when it came back online. Rabbit knows which client it has already routed to and where messages went. Kafka is not that sophisticated in that regard. Kafka has been described as "dumb broker/smart clients" while Rabbit is "smart broker, dumb clients."
3) The scaling. Rabbit is very scalable. Once you get to the Uber/Paypal level (like, a couple of million writes per second), then Kafka becomes the obvious choice. Rabbit handles thousands or writes per second just fine. However, at that second company and like many others, they thought they'd have to suck up all the data, so of course, Kafka was the more scalable tool long term. Spoiler: We were never, ever close to PayPal-level transactions. If the size of the sun represents paypal/Uber transactions, we were basically Manhattan.