Why does a Kafka consumer track its own 'offset' instead of the broker tracking what each consumer has read?

Storing the offset with the consumer (in an internal Kafka topic, `__consumer_offsets`) lets each consumer group track its own independent read position on the same topic, and lets a consumer resume exactly where it left off after a restart or rebalance — the broker doesn't need to know or care which consumers exist, keeping it simpler and more scalable.