True, many peoples join different projects and try to work on them parallelly hoping to gain more profits than just working serious and on a single one but they find themselves in a bad situation as you mentioned, not being able to coordinate between them and lacking the time to finish what they are supposed to do. If someone has the potential, time and experience needed to do that and be able to provide a good quality work that's good but the majority of us can't do it so it is better to stick to one project and work hard, use our skills and put real effort in order to be worthy of the reward.