People care less about large groups of people than individuals, per capita and often in total. People also care more when they are one of very few people who could act, not part of a large group. In many large scale problems, both of these effects combine. For instance climate change is being caused by a vast number of people and will affect a vast number of people. Many poor people could do with help from any of many rich people. Each rich person sees themselves as one of a huge number who could help that mass ‘the poor’.
One strategy a charity could use when both of these problems are present at once is to pair its potential donors and donees one-to-one. They could for instance promise the family of 109 Seventeenth St. that a particular destitute girl is their own personal poor person, and they will not be bothered again (by that organisation) about any other poor people, and that this person will not receive help from anyone else (via that organisation). This would remove both of the aforementioned problems.
If they did this, I think potential donors would feel more concerned about their poor person than they previously felt about the whole bunch of them. I also think they would feel emotionally blackmailed and angry. I expect the latter effects would dominate their reactions. If you agree with my expectations, an interesting question is why it would be considered unfriendly behaviour on the part of the charity. If you don’t, an interesting question is why charities don’t do something like this.