CiviCase - Edit Actions with permission: "CiviCase: access my cases and activities"
It was done deliberately in 2010 and it's been that way ever since. While it's not stated in the JIRA link below, if I had to guess the reason it's because it might allow you to give your buddy access to a case they shouldn't see.

See


https://issues.civicrm.org/jira/browse/CRM-5666
https://github.com/civicrm/civicrm-svn/commit/d3cc0a1d87d86bbdc5eeda2a8975e382fcf66576#diff-33fb19b4d7d2903e556b3c4a2ed1ffd5L129-L130