Since they'd be able to e.g. unblock people. Note that right now this is the only way for a sysop to unblock themselves if the AbuseFilter blocked them. While, as pointed out in T232908, the actual solution to that is checking user_groups in all filters, it'd be good to have an "emergency button".
Maybe, we could add a quick button like the one for restoring autopromotion, or we could make /revert only revert blocks involving the current user.