Because it appears to be a requirement. Unfortunately SSH does not look at /var/lib/sss/pubconf/known_hosts:
debug3: mm_key_allowed entering [preauth]
debug3: mm_request_send entering: type 22 [preauth]
debug3: mm_key_allowed: waiting for MONITOR_ANS_KEYALLOWED [preauth]
debug3: mm_request_receive_expect entering: type 23 [preauth]
debug3: mm_request_receive entering [preauth]
debug3: mm_request_receive entering
debug3: monitor_read: checking request 22
debug3: mm_answer_keyallowed entering
debug3: mm_answer_keyallowed: key_from_blob: 0x561842345040
debug1: temporarily_use_uid: 1683000000/1683000000 (e=0/0)
debug1: restore_uid: 0/0
debug1: fd 8 clearing O_NONBLOCK
debug2: hostbased_key_allowed: access allowed by auth_rhosts2
debug1: temporarily_use_uid: 1683000000/1683000000 (e=0/0)
debug1: restore_uid: 0/0
debug1: temporarily_use_uid: 1683000000/1683000000 (e=0/0)
debug1: restore_uid: 0/0
debug3: mm_answer_keyallowed: key 0x561842345040 is not allowed
Failed hostbased for admin from 172.26.0.1 port 55634 ssh2: ECDSA SHA256:wJ0OVmkiVnMjuoiRe5sdBVz5sMTTKIbYRWorTk+CnUQ, client user "admin", client host "hpclab01.cluster.iq.ufrj.br”