Backes is currently 32 years old, putting him way on the wrong side of 30 to be getting paid $6 million a year. His production overall has also been slipping. While still an effective player who brings size and heft along with a netfront presence, Backes turned a good playoff run into bank with a team very much looking to add a heavy player.
Backes should be a good fit on the Bruins; he would've remained a good fit on the Blues. However, the money and term would've potentially added to the Blues' already precarious cap position.
The Blues lose a locker room leader, certainly. However, it is easy to question if a solid playoff season should define a captain's reputation after years of poor team performance. Until this season, Backes was on the scoresheet more than often not in the PIM column, not the points column. It took him until this season to flip that trend.
It's disappointing to lose a long-term team member and captain for nothing during free agency, but paying $6 million a year for someone who had all but slipped to the third line on the Blues is difficult to justify.