I am not entirely sure how all this works, but the moderators that approve comments are Itch staff. That's why it takes so long. They are bogged down with all the issues caused by the criminals.
It might be, that developers also can approve comments on their own game. If they manage to find the button for it. But as far as I know, only community style comment sections are moderated by the developer.
As a side note, one of the reasons why there are no private messages on Itch is the "moderation nightmare" this would entail. Imagine the fake accounts spamming users directly.