I mean one unsubstantiated armchair take: it's newer than Rabbit / Kafka (RabbitMQ was built in 2007, Kafka in 2011), since then the learnings from distributed systems, message queues and programming languages has improved by leaps and bounds, and the existing ones will have backwards compatibility / legacy issues.

That said, there are indeed plenty of commercial and noncommercial alternatives, so now that it's been published I'm sure there will be some thorough people making comparisons soon!