I think there is one reason why Humphries isn't playing and that is, we have no interest in trading him. We don't want to take back 12mil in salary, we need that coming off the books. Nobody can take 12mil straight up off our hands for a trade, so what is the reason we'd play him?
We need to trade Bass, so he is playing to hopefully make himself tradeable, and Vitor, Sully, and Olynyk need playing time to develop.
If we don't make any trades this year, next year we have 20mil coming off the books and a possible trade exception to play with for 10mil or whatever the Pierce amount was. We also might get the #1 pick or at least a top 4, so we could get pretty good quickly if we aren't burdened by extra money.