To bring good players in, you have to move players out. When you’re buying specifically, you have to move out pieces that have tantalizing potential to a team in a rebuild or can at the very least fill a lineup spot for a few years with a chance to develop into something more alongside picks and/or prospects.
While the Calgary Flames have ample prospects and most of their top selections still in their possession, a lot of big trades often involve a younger NHL player as part of the returning package to the team dishing the prime talent.