Later when all the tell-alls were written about Diana, everyone, across the board, said she was committed to her charities and sought out meetings, many never reported or photographed, with people in need, and often she said that they actually ended up giving her strength/comfort.
So despite all the major, emotional, and humiliating battles she fought at home with Charles and Camilla and the BRF, Diana still dug down deep, wiped her tears, and went to work giving her all to individuals who suffered, she thought more than she did, or as much as she did. There is nothing to critize about that! Diana had weaknesses, but not when it came to work ethic.
Kate on the other hand, just wants to be a rich man's wife, one with invites to the best balls in town, those that require an expensive new frock. More like being the Lady of Pemberly, Mrs. Darcy Fitzwilliam, rather than anyone or any position with more serious expectations attached to it.