I don't know about other philosophers, but their reluctance may be motivated by thoughts such as those Gerald Gaus expresses in his essay "Should Philosophers Apply Ethics?" in Think (2005), pp. 63-67, available at
I am involved in a new organization called ASAP -- Academics Stand Against Poverty -- which (in a soon-to-be-posted essay) has examined and argued against Gaus's arguments and is now very actively doing the kinds of things that Gaus warns against. You can find some relevant material on our website www.academicsstand.org. You will there also find that one of our current projects is "Climate Voices", a project that focuses on global warming and its effects on people whose home environment is made uninhabitable thereby. This project is, by the way, essentially run by students.