The issue with smaller startup or charities is that they don't have the means or time to employ and test someone for a few weeks. It's sad to denote, but there really are very few developpers that actually have the competence to stand on their own / manage themselves in smaller teams. So that's why they do it.

If you don't have something concrete that you built to show, there are big chances that you will have take home work.

But the sleeping bag culture is dumb, and there is no excuse for it.