This is a simplistic take. Kafka isn't just about scale, it, like other messaging systems provide queue/streaming semantics for applications. Sure you can roll your own queue on a database for small use cases, but it adds complexity to the lives of developers. You can offload the burden of running Kafka by choosing a Kafka-as-a-service vendor, but you can't offload the additional work of the developer that comes from using a database as a queue.
This is a simplistic take. Kafka isn't just about scale, it, like other messaging systems provide queue/streaming semantics for applications. Sure you can roll your own queue on a database for small use cases, but it adds complexity to the lives of developers. You can offload the burden of running Kafka by choosing a Kafka-as-a-service vendor, but you can't offload the additional work of the developer that comes from using a database as a queue.