In Campbell what the Blues would be getting is a guy who, when he brings his A game, is widely acknowledged as one of the NHL’s best goalies.
Sure he hasn’t worked out in Edmonton, but Campbell has played in Dallas and LA before, so he knows that there is typically less media scrutiny in most American markets, save perhaps for New York and Boston. He would get a chance to reset his career in a quieter market.
If the rumours of Binnington having a temper are true, then Binnington will become more and more of an embarrassment to the franchise the longer he stays in St. Louis, which naturally would decrease his trade value, so it would be smart to trade him for what will probably be the best haul you can get. It’s frustrating for veterans playing in a losing environment when they’re used to winning like St. Louis is.
This is a chance to get rid of a player who is becoming more of a thorn in their side and replace him with a humbler player who would fit in better, and with the better psyche Campbell would own playing in a place with less scrutiny, there’s a better chance you get the good game of Jack Campbell. The cap situation wouldn’t change at all for St. Louis and he gives them options as a franchise.
If his career rebounds as expected and the Blues decide to start a rebuild, they can trade him for a big haul and trade/sign someone cheaper to take his place. If they decide to just retool and tweak, they can keep Campbell and he can be their starter for the remaining four seasons of his contract.
If he falters they’re no worse off then they were before. It’s a calculated risk that in theory at least has the chance to pay big dividends to them.