Enable manual user registration. I have one of my sites moderators review each registration because we get a lot of spam too. Using Cloud Flare has helped with that a lot too because it allows us to restrict spammy IPs. I run a MyBB forum but I'm sure a simple machines forum has similar Plugins that make it hard for bots to register. At the end of the day, you're driving away real people who want help with their condition because they are too annoyed to want to post. This forum is dissapointingly empty and I suspect that is the primary reason why.
Interesting suggestion, but not applicable here. When I first arrived here, and than became a moderator, we had around 200 registrations a week, and about 14000 members, and only 650 of them were legit, real members, the rest were spammers accounts. Bots are attracted here because we use a lot of words like "orgasm", "semen", prostate", "masturbation", and so on ( which, I guess, may not be the case on your forum). we often had porn threads created overnight, spamming the forum. Now this is over, as well as the 200 hundreds false new members a week.
We do not have the resources to manually review all the applications. If you, or anyone else, are interested in taking the responsibility to do this approval work manually, just contact me. For now, our limited resources are highly needed on other essential tasks.
And, keep in mind that registering is only needed for posting - all forum content is accessible to anybody, member or not.
Apart from that, this forum is not empty. Keep in mind that POIS is a very rare syndrome, and not well known to the public, so it wouldn't be normal to have those 14000 members we had when I became moderator ( that is exactly what led me to take a closer look at the registrations and the registration process). I have POIS for around 40 years now, and found this forum only 5 years ago. I was quite surprised to not be the only one with this, and many others have that same impression, because POIS is not very much talked about. Slowly, things change and POIS sufferers find us.
However, this is not like having a forum about old muscle cars, or about a disease like asthma, or any subject from mainstream culture. We will not attract attract people by the thousand. And, above all, members often undergo extreme fatigue and/or cognitive problems, due to POIS, which keep them from participating more on the forum.
Questions have been made easier lately, so this will help with the process. Anyway, if any problem, my e-mail is showed during the registration process, and is also written in a specific thread on the Technical Support Board. So, anyone can e-mail me at quantum "at" videotron.ca ( just replace the "at" by @ , of course
) if they have problem registering.