Perhaps the administrator sees that no violations are currently occurring from this account and simply gives it some concessions for presence on the forum.
I wouldn't be surprised, because I thought something like that. If in practice and with a minimum of precautions someone banned can create a second account without being detected, rule 25 is often impractical. Now, if a ban evader is detected and in the account he is using now he is not breaking the rules, does it make much sense to ban him? If you ban this account you know what he will do: create another one. And surely this time he will be more careful until the time comes when he will create an account that will definitely not be detected as an alt of a banned account.
Surely it is more relevant what he is doing now with that account, if he is respecting the rules.
What I don't understand is some specific cases, like Polo7 and his alts, who is not only a ban evader, but he also keeps shitposting the forum.