Nothing surprising there. This is the historic method of controlling your people in Africa,and the whole purpose of that concert and album was to pump up musical careers,especially those of Michael Jackson and Quincy Jones. It was probably good for $100 million each in international sales of their old and new music. You just can't begin to buy publicity like that.
The other musicians most likely did it without thinking because it made them feel good and noble. I doubt any of them ever gave a moments thought to what happened once the attention went away. They just ASSUMED the hungry people would be fed.