A problem to be solved is better than a mission to sustain (or save).
And when marketing philanthropy, raising money for a nonprofit, or advocating a mission - problem and solution outperform "help us keep the doors open" - not even close.
Focus on a project that has a solution, an outcome gives the giver more control (or at least the appearance of control) than a "give us your money and we'll do great things with it" message.
Sustaining a mission, supporting good people doing good things, and even paying overhead expenses are weak seconds in persuasive communications. And any explanation or justification offered will, be necessity, focus on the organization - it's virtue, it's mission statement, it's sacrificial staff, but not on any measurable outcome.
That is, it may be an organization's problem, but that's not our problem. And following the money shows us that clearly - so why do so many miss it?