The ALL keyword is misleading in RESET REPLICA ALL because it works on a single slave.

The ALL also resets the PORT, HOST, USER and PASSWORD parameters for the slave. If you are using a connection name, it will permanently delete it and it will not show up anymore in SHOW ALL REPLICAS/SLAVE STATUS.

Versus the ALL in SHOW ALL SLAVES STATUS means to look at all slave connections

ALL SLAVES (or ALL REPLICAS from MariaDB 10.5.1) gives you a list of all connections to the primary nodes.

This ticket proposes an alias for the ALL in RESET SLAVE ALL to remove the chance of intrepting the behavior as resetting all existing slaves. For example, RESET SLAVE ['connection'] PURGE, to be more clear that the slave is being deleted entirely.