I do not know what the team proposed to the managers, but they need to realize that if they want to advertise here, they need to allocate certain funds for the marketing which includes the manager's fee and the participant's payments. No one will be willing to work on the condition that if we can bring you sales, the gambling team will pay us and if there is no sales, there may be no payment. Also, such a model is not transparent because the site can always show fake stats in order to avoid or lower the payments.
They need to think that so many trusted gambling sites are advertising through signature campaigns for long time, meaning that the ROI to advertisement on this forum is good one.
OP did not know or did any research on how a signature campaign works here in Bitcointalk, what he is proposing is for the manager to spend their funds and they will do a profit-sharing, they don't need a signature manager all they need people who will promote their project on their own.
Checking their business model, it is profitable for affiliate marketers but no bounty manager will accept this kind of scheme, if OP is the main developer of the project then I agree that he spends his own funds and gets 100% of the profit, so why not try a month campaign and see the results, you can repeat if the campaign is successful.
Maybe they don't have money to spend on those campaigns that's why they don't think its good option for them especially if their fund is limited only for rewards of their potential winners. Then I guess if that is the case and they can't hire good managers to help them then maybe their development will became so slow.
Also for sure that affiliate marketers would never try to risk their effort made on unpopular betting site since for sure they will not waste their time on what they think not sure for them so provably a lot of people will go to reputable casino since there would be more higher chance that they get their payment what they deserve to have. Maybe they should try to risk on the option you suggest since maybe they can get more exposure in this forum with running that campaign.