Why http client error for health check on standby instance of vault?

In the documentation I see that you will get a 429 Too Many Requests when you visit the path /v1/sys/health on a standy instance of Vault. What is the decision behind the fact that Vault wil send a response with a http client error status code when checking the health of a standby instance of Vault and how is it meant to be used?

Standby nodes do not service requests, so this return code encourages default configurations of loadbalancers to not route requests to them.

Thank you for your answer.