Nowadays bounty campaign became an opium for most of the investors, comparing to the strategy of promotion in recent years it doesn't look fragile, nevertheless, it is not quite convenient for the busy ones, who can't spend their time on promotions.
It also uses participation encouragement, and it's biggest advantage is rewarding you based on the effort you put into the new project.
All the same, it's just a small part of the project, which stimulates people who have lots of free time to spend it with benefits.