I could tell you the reason why to disable comments. Sometimes there are several hundreds pictures in gallery and people watch them clicking 2-3 times per second: next, next, next. This could be faster then processing requests like
GET /wp-admin/admin-ajax.php action=get_attachment_comments&nonce=….
On the server side the request queue and server load grow and grow and after a few minutes user is blocked as DOS attack (if you are lucky and have DOS protection) or your server have problems for some time.
I know that thoughtless clicking is stupid and such idiots deserve blocking but your code could be foolproof and disabling comments, particularly when you do not use them is wise solution.