Why would you put all your time and effort into a project when you aren't sure you have the team to actually out into motion?
Because we as creators simply want to create, regardless of what stops us.
Why are you seeking collaborators if the project is already fully baked?
Because we want to see someone skillfully execute our idea for us, and getting someone to work with us takes a convincing, well-thought plan.
Why would anyone join a collab where most of the creative work is already done?
Because there are tired artists like me who just wanna draw without putting mental effort into thinking up story. The only reason I offer to draw for collabs is because I trust that I ONLY have to do my part as an artist, and nothing more.