They like GR3 enough to have drafted him. They clearly view his potential production as more valuable than whatever a theoretical Barea trade could bring in, considering that one's expressed interest in acquiring him.
There's also the very real possibility this is a mutual separation, while Turiaf might have no problem with his role on the team.
Well, as mentioned from a financial + trade asset point of view it makes no sense to me.
Things outside of that, then anything goes and I have no problem with it. I have no problem with them keeping Robinson over Barea under the circumstances.
Yet, I feel that eating up $4.5 million is not a wise thing to do. I'd just send him home and cut Turiaf, saving a few million in the process, potentially more later on if you find a taker with cap space or a trade exception that suddenly has a need for someone of Barea's talents.
But whatever, there are no tax implications regardless so might as well treat it as a sunk cost. Personally I wouldn't do it, but it's not my money... I'd cut Turiaf.