Because of your reputation? Isn't it better to be known for one awesome project that did something amazing for the community and came out soon after announcement and had everybody cheering, than be known for four projects, of which three were failures, and now you're known as the guy that can't follow through on anything and whose projects are all bogus? Instead of being only known for something great, so you always get support when embarking on a new project?
Basically if your rep is that you follow through with your ideas with a plan, people are going to want to collaborate with you because they want to be part of a great project, if you're known for great and successful projects. If you have the rep that you only do things half-heartedly or you don't think things through and make proper plans before beginning a project, people aren't going to want to collaborate because it's a huge waste of their effort to spend hours or days or weeks on something that was always destined to never see the light of day.
