⭐ Merited by NotATether (1)
Selling their license keys is prohibited by the Malwarebytes Software License Agreement. Therefore, it's quite possible that theymos itself banned those who were selling keys and deleted their threads 
Side note, isn't that the case for pretty much all AV software? None of them like it when you resell their keys.
Why isn't it prohibited to buy and sell keys for all types of anti-virus?
The thing is that the license keys are impersonal goods, so to speak. That is, in order to get and subsequently use a license key, you do not need to go through KYC. In addition, on websites and forums that distribute warez you can easily find generators of license keys to various programs. And finally I want to say that, in principle, selling license keys is quite a legal business, which is engaged in many resellers of digital goods. Well, of course they get these keys in a legal way.