Depending on the implementation of a pay-to-comment scenario, it could still be profitable for the scammers to pay. They would definitely be tracking CTR or whatever their equivalent is on scam campaigns.
In this case, the scammers are all using similar profile photos, so that part of the whack-a-mole seems like easy pickins. At least at creation time, they could fuzzy compare the profile photos of the commenter and the channel. And compare among other commenters.
The scammers would definitely move on to something else, but it seems like the scammers are scoring a lot of really easy wins right now.
I hate scammers and I love ruining their day, but this is one of many areas where I can't give more attention to it than the platform can.
Could grandfather in existing accounts, and have existing accounts give references for new accounts to continue getting "free" accounts. The cost being a loss of the ability to "mint" new accounts if any of your existing referenced accounts start spamming.
So you want to comment with your new account, you either need a "mint" from an existing account, or you need to fork over... let's say $50 to activate comments. (Amount could be whatever).
I remember when domain names went from free to $70 under network solutions. This was meant to be cheap but really limited people who could register domains.