We don't know that yet, I already got a feeling that they just used this Cryptotalk campaign as a stepping stone to gain some participants in preparation for this "InvestBox" investment scheme.
It can be but I think they needed strong promotion for the Cryptotalk forum. And for the wide promotion, the Cryptotalk forum has thousands of regular posters now! Therefore people can earn a penny by posting in that forum too, so posters are stable. But when Yobit realizes that the forum has enough members and it's growing they come out from their good musk and open the scammy invest box, lol!
If they want a "strong promotion" for the Cryptotalk forum then why do they need to change their signature campaign from Cryptotalk to InvestBox? Why not have a separate campaign for each one of them and not force their existing Cryptotalk participants to change their signature to Investbox? That's what is bugging me on how Yobit without any kind of notice suddenly change their signature campaign. It's like an already existing signature campaign for an ICO project suddenly changes it's course and promote a gambling site which totally doesn't make sense for both the participants and the campaign manager.