Schema evolution

[pipihunk]

Have some questions on how consumer uses avro schema. Basic workflow is producer includes the id in message and consumer uses that id to get the schema from registry. My question is on schema evolving issue.
Since consumer uses the id to get the schema and for every evolved schema, a new id is generated on producer’s side, why are there compatibility issues on consumer’s side if consumer can always get the updated schema based on the new id from message?