He's of of the top ten goalies in the league, that's where.
That said, I agree that Mrazek and Ouellet would be an overpayment. Couturier's future potential is by no means assured either, and his level of play this season greatly leaves something to be desired.
Signing DeKeyser and giving him a shot is better than doing nothing and letting him go to another team. Especially with the Lightning in on him, who we'll be playing with next year and already signed Andrej Sustr.
DeKeyser could very easily come in and play for the Red Wings immediately. They have a lot of bodies on defense, but with Quincey out, that 6th spot is quite attainable right now. White is horrible and was a healthy scratch for a long stretch. Huskins is a nice depth player and Colaiacovo is always a health concern.
Stocks in Detroit area hospitals set record highs in price when his signing was announced.