Why can't you have more consumers in a group than partitions?

Each partition can be assigned to at most one consumer within a consumer group at any time. This is by design: multiple consumers reading the same partition would create coordination complexity and ordering ambiguity. If you add more consumers than partitions, the extra consumers receive no partition assignment and sit idle — they're essentially warm standbys waiting for a group member to fail. To increase consumer parallelism, you must first increase the partition count.

Expected key concepts: at most one consumer, partition, coordination, ordering, idle, warm standbys, parallelism, increase partition count