reason why sys, system and sysman accounts are kept open

 Hello,

We are going through audit and auditors are asking for a reason why sys, system and sysman accounts are kept open, not locked or locked and expired.

The DBAs on our team have DBA role granted to them.

The user SYSMAN is used by the DB console.

Could somebody give me a good reason/argument why these three accounts need to be kept open, which can satisfy audit?

Thanks in advance!