If you ban knives they will get guns from the dark market, thus, if you make ranking hard or impossible, people will just buy accounts or merits
Indeed the only ones who profited from what admin did were accounts farmers, they received free merits and can now sell overpriced accounts
Doing so also makes the amount of people doing so smaller.
Not everyone has money to spend on this.
You can never control everything. The idea is to limit it as much as possible. And this is working pretty well.
Also most account selling occurs on forum and account is tagged which greatly reduces what you can do with it afterwards.