This is a bit offensive for user trying to help.
Deleting an account is not an available option on all the casino I’m using. Only self-exclusion that leads to permanently banned is always the path which the support offer for user that doesn’t want to use their account anymore.
It’s probably to retain user records to avoid bonus abused. Think about someone using all the bonus then delete the account records then create new one to avail all bonuses since casino doesn’t your records. This is one of the reason why casino only banned account permanently instead of deleting the account records.
I hard an experience the last time I self excluded myself from an online casinos, very popular in my country and at that time I wanted to reconnect back later and the casino outrightly told me that my account doesn't exist, and when try to create a new account, it wasn't possible since their rejected my details anytime in insert them, since it has been used before, so most casinos that offers accounts deletion or self exclusion have a highly strict standing that prevents and exit the gambler from the casino forever.