During the launch of any project, none of the participants knows for 100% whether the project will succeed. You ask why to support new projects, in my opinion this is a strange question.
After all, support lies in the support itself. You support the project in which you believe and hope that he will succeed.
You offer assistance to the project in order to help the team realize their idea.
Will this work out? Unknown If you do not believe in the project and support it only for the money that you can get later, then it is not surprising that the projects do not succeed.
First of all, yeah people can make some sort of prediction and know if the project will succeed or fail. If the person does a deep analysis of the project, they can have a pretty good idea if the project is just a sham or legit. They can have a look at the developer team, what they are proposing and how they will proceed. If they have any slightest doubt about anything on the project, then I recommend them to stay away from the project. Highly likely the project will fail.
Just blindly supporting the project just because you "believe" on them is totally a wrong thing to do. All you would end up doing is support and encourage more scam projects.