~snip~
Make no mistakes, i detest their shilling and i don't know why an exchange would advertise in this way, but i am basically telling you why they are breaking no forum rules, which should be easy to understand.
I would not agree that what they are doing is not against the rules of the forum, because posts in which certain members systematically shill someone or something are something that will definitely be deleted if it is reported to the moderators with concrete evidence (post history). There's no justification for this, least of all your explanation that they're staying on topic so they probably have a justification for what they're doing.
They advertise this way because it costs them practically nothing except worthless tokens. It's a kind of bounty campaign, you get instructions on what to do, then you send links to a manager who counts how many times you mentioned their company.