To some extent, one doesn't even see the competent non-profits. They don't market aggressively, they don't scale up rapidly, they just stick to their niche and quietly hammer away at it for decades on end (often on things that have no feasible exit, like schools that will need to be externally funded forever)
That seems like a simple money regulations issue. If the school has a $100 million endowment, but doesn't spend into it, the school would exist forever. If we say 10% returns a year, that's $10 million to spend on students in the form of teachers and classrooms and housing and books and everything. Unfortunately, that only teaches N students per year. But it would last ~forever. If, however, you get greedy with wanting to teach more than N students per year, then you get into the treadmill of needing external funding forever, but on the face of it, I don't accept that external funding is required forever.
A 100 million endowment is effectively "forever funding" from the perspective of a school that takes in maybe 200k/year of donations. You don't get 100 million endowments without the scale and marketing, unfortunately