Development by donation takes some die-hard user enthusiasm. Consider Litecoin - no self funded development, huge user base and transaction volume, supported by almost all exchanges and it has still gone through periods where the developers couldn't justify the time required to maintain it. Other projects, like promotion and merchant adoption, face even great difficulty in securing adequate donations. The typical volunteer opensource development model is all well and good but as long as people are prepared to accept that developer talent is worth something, crypto currency provides a very nearly built-in way to bypass the unreliable donation method of support.