Kafka is one of those systems that needs to be justified by out-scaling other solutions that don't come wedded with all its baggage.
Lessened somewhat with SaaS products like Amazon Kinesis (technically not a Kafka, but close).
Another "baggage" is that an event-driven setup is eventual-consistent -and async- by nature. If your software already is eventual-consistent, this is not a problem. But it is a huge change if you come from a blocking/simple "crud" setup.