It's a just a dumb cranky way to be as a fan. Truth is the same is true of Taijuan Walker, he doesn't stink, age and injuries merely caught up with him sooner than we would have liked. Ditto Ryan Howard. But agreed, Robertson never "owed" the Phillies anything when he came back, other than his services to the best of his ability and health at that time. Whether he was a good signing last year is questionable of course, but the price (no trade, prorated money) was right.
I suppose it suits the front office when fans blame someone like Tartabull, instead of them (though he had a perfectly good season the year before even if that had been more of a bounce-back/outlier. Actually pretty sad the injury ended his career).