It's very hard* for established, millionaire artists to pull off things like this without looking like fucking Bono and at the same time, if they do nothing, they will be criticized for that too so it's like what can they do? As much as I hate Bono, I think it's better they do something than nothing at all which is why I view criticism and people questioning the motives as somewhat irrelevant. Will there be money for the cause? Yes and isn't that ultimately more important than any perceived motives?
*"hard" here is obviously not a "real" hard, more like an I-land "hard" but still...