What you experienced was called "Self banning"! Here you can learn more about this,
ACCOUNTS WILL BE LOCKED IF THE SECRET QUESTION IS USED TO RECOVER ITAs far I know, you
MUST sign a message to prove your ownership in order to recover your account. But I don't see any address linking to your account as yours is a casino representative account. Not sure how it would be resolved at this point.
Unfortunately, not everyone knows about this. Otherwise, people wouldn't use the secret question to recover their accounts.
My question is: why doesn't the SECRET QUESTION option on the forum disappear? Or at least it doesn't get blocked forever?

This would be a way to prevent people from using this option when it should not be used.
According to achow101, theymos made it this way so that when someone (probably a hacker) tried to guess the secret questions using the leaked database from 2015 (you know which), the account gets locked. This was probably a failsafe or a precaution to prevent anyone from guessing the secret questions.
