I doubt anyone offered anything worth trading those controllable players right now.
You don't trade current starters on a team that's turning it around for second tier A ball prospects, that's just silly, because at best they may become the same players you traded.
McGarry was a great pickup for Benoit, he's doing something this year, lights out in the FSL.
He was an 8th rd pick, MLB.com rates him the No. 147, BA at #270, JR out of FAU, so he's not some college senior RP.
He's had medical issues (his first couple years of college were interrupted by a stress fracture) and is probably more likely to stick in the 'pen. He can reach into the high 90s, and normally hovers in the mid 90s, and MLB.com suggests he could make it to the majors rather quickly.
Just adds more depth to the minor league pitching, and RPs have funny career trajectories, they often take longer to arrive, then suddenly the light goes on (or off).
Phillies threw cash in, which is how they got a real prospect for Benoit.