It is ultimately a way to further cripple 3rd part apps. Thus, making the official Reddit app look better by comparison. It’s not certain if Reddit will get rid of porn, because while porn sub-reddits don’t generate ad revenue, a not insignificant portion of Reddit’s user-base visit porn sub-reddits, making Reddit a good one-stop-shop for a user’s media related need. So while porn doesn’t generate ad revenue, it brings users, users who also visit other non-porn sub-reddits that do.