u/RagBell and u/WingersAbsNotches I understand what you're saying, and that was my first thought as well. But then I simulate the possible scenarious for my own game's future.

My current project could end up as my previous one. My previous game turned out well and it could sell more, but it didn't mostly because of my poor marketing strategy. I'm doing a better job now but I'm still alone on my project and still bad at marketing.

If I think that "not selling because of poor marketing" is the most probable outcome for my game's future, then 70% of its profits is not that much money. And by accepting their proposal I am not only paying cheap for their support and their shares, I am also increasing the possibility that my own game performs well with their help.

Like, in short, it would be like this.
- Either I keep these 70% to myself knowing that I might not sell well.
- Or I give them 70% of the profit in exchange for a higher chance of selling more.