All accounts have a number to it, if we remove one whole line out of the data base there can/may be problems which will arise from it. So it is better to just leave it as is rather than remove it completely as well.
Besides, when numbers go in order, it's best since then no numbers are missing for when a new account is created. New accounts created will have the latest number instead of filling in the blanks of the deleted accounts. This way we are able to keep track of who has just signed up for an account etc.
So instead of having 1, 2, 3, 4, 5 etc. If we delete an account, it would be 2, 4, 5. When someone creates a new account, instead of it being account number 6, it becomes account number 1. It just gets messy this way.
But really, if someone is banned for botting or scamming or something, does it matter if the account is deleted? Banned means banned. There is no "re-accessing" the account or unbanning if you are without a shadow of a doubt, guilty of the crime committed. Ie: If you did something bad, you will never be able to access that account again.
