I think the issue here is that a 503 from other calls is not an expected regular outcome for operation. The bulk endpoint explicitly uses 503 (and in more recent versions 429) as a code to inform the client that the bulk queues are full and to try again later. The other endpoints are not likely to return this status code, and thus we break eagerly since it could be a configuration problem that should be fixed, a party in between the client and server has deemed it fitting to return a 503 which is disruptive, or the server is legitimately unavailable.