We are now using a new captcha system which should help stop spambots from ever registering in the first place. Previously we were using ReCaptcha which has unfortunately, been cracked by said spambots, leading to difficulty in telling which users registered legitimately in the past several months, amongst the flurry of spam registrations.
To deal with the bots that already registered, it was necessary to purge all registered users who didn't have an approved post in the past several months. However, now that the captcha has been changed to an effective alternative, it should now be safe to register accounts without worrying about them getting purged.
It is recommended still, however, that new users make an introductory post just to confirm you are human, thus helping if the new captcha gets cracked by spammers in the future.
My apologizes to any legitimate users who may have had their accounts deleted, but there have been no bans dished out during the purges, so registering again should be unhindered.