From a Flyers perspective, there is too much effort and time placed by the organization in acquiring and stockpiling prospects to give them up. While none of them may ever play a game in the NHL (or in the case of Morin, another game), there is too much risk for the Flyers to give up Frost and Farabee. In many lists, Frost and Farabee are 2 of their top 3 prospects (along with Carter Hart). Next to Hart, Sandstrom is the Flyers best goalie prospect, and on a team where goaltending never seems to be solved, it would be better if they held on to him.
Defense is the Flyers strong suit in prospects, so acquiring a solid d-man, while enticing, doesn't help their long term need, which (assuming the d prospects pan out) is really the area the Flyers need to work on.
The Flyers are looking long term, and while Barrie would make them a better team immediately, long term he wouldn't be as helpful as the upside of these prospects.