As far as I know, Roobet does not conduct any marketing campaigns outside the forum, and all (or most) of its strategy depends on the bitcointalk community. I agree with you in suggesting that they can diversify advertising plans, but not by changing a successful one.
Roobet actually does advertise their services through social media sites like Twitter etc and don't just depend on Bitcointalk. Also, no one apart from their team knows whether their marketing forums within this forum have succeeded or failed.
I don't remember seeing any ads for Roobet on any platform outside the forum. You may think that it publishes updates on its channels on these platforms, but this is different from managing an advertising campaign with all its costs.
At a certain time, there were platforms that ran advertising campaigns only through the forum through signature campaigns and competitions. When there was a lot of traffic, the forum alone was sufficient to achieve the desired results of the marketing strategy. But this has declined significantly, and almost all that remains is Roobet that is adopting this strategy and which is certain to achieve the desired results.