They are not responsible per se, although you could claim rich countries have a responsibility towards poorer countries to help out. However, the way they stopped funding these projects, abruptly and without warning, means that other funders can’t step in in time and charities organizing this help have no way to find solutions before people die. It is unnecessarily harmful.

As a sidenote, many issues charities are trying to help with are caused by climate change (for which richer countries are responsible in larger part) or past colonialism/exploitation by these richer countries, so they do have a responsibility.

This is all general stuff and not specific to this example…