Hey InboxReads creator here. I've been facing the same problem with other newsletters submitted to the site so I think you're right that spammers are scraping directories.
I've added a bunch of mitigations but found that they're faking the referrer when subscribing to newsletters and not even going through the site anymore.
Captchas do solve it though!
But I'm just as baffled at their endgame as you are.
Not a huge proponent of dark mode, but aside: resent the use of Hackers pic on this post. Dade Murphy was wearing sunglasses in the opening scenes while hacking!! Wasn't just for an elite look!
I've added a bunch of mitigations but found that they're faking the referrer when subscribing to newsletters and not even going through the site anymore.
Captchas do solve it though!
But I'm just as baffled at their endgame as you are.