It's a good question and I don't get it either. You are seeing a team that could sure use some extra speed, a jolt and some scoring and you are sitting on 3 of the top scorers in the NHL. The logic is getting really really hard to support.
And honestly don't give me the "ya but they may only play 4th line" argument as I don't buy that. First the Flames 4th line is garbage as it is and when you have a coach who wants to roll lines that's a problem, so if a young player can help there then let him. In addition to that I don't buy this argument that players can't develop there. Mang came up, played 4th line, was a really positive element and then moved his way up the lineup. It's just on the coaching staff to make sure they play at least there 5-8 mins but I would argue that 5-8 mins of ice time in the NHL is going to better develop the likes of Phillips, Zary and Pelletier more than continuing to play in the A. All 3 of those guys have shown that they can handle that so it's time for the next step.
No matter the prospect there is always going to be development at the NHL level. I think the whole "the NHL is not a development league" is one of the biggest farces in the sport.
The lack of playing young players is just one of the tradeoffs you get with Sutter and I get that, but I'm really surprised at the level of favoritism he is showing to certain elements/players of the team this season. Sutter is intentional so i can buy that it's part of the bigger plan but I have a level of concern about it for sure.