Because Kafka is not a message queue, but can be used as one. Multiple consumers on a topic is the default behavior because it’s very useful for the typical use cases in Kafka. I like to think of Kafka as bringing “micro services” to data processing. If I want order data to be both shown real time on a dashboard as well as aggregated for reporting purposes I’d build two different consumers for the same topic. One which sends the results off to the order dashboard via websocket and one which performs a rolling aggregation using a streaming query most likely. Maybe you now need to alert the sales team when an order comes in over a certain amount so they can give the customer the white glove treatment. Just add another consumer which is a ksql query for orders over $$$ which then get dropped into the high value orders topic. There you can have a consumer fire off the email to the sales team. Want to do other things when a high value order comes in? Add another consumer.
