Reimer was like 35 when it happened. Mackenzie is literally in his prime. Also, from what I remember there were offers for Reimer at the deadline and DW didn’t go for any of em. Reimer also, with the exception of last year, was consistently good, never having a save percentage below .900 prior to last year, which, as we’re seeing this year, is probably more a product of the awful defence than anything. So far this year he’s looked as good as he’s ever looked in detroit.
Lastly, no one would be bringing him in to be their starter. Merely someone reliable that can spell their starter if needed for any reason. Bringing in a guy like Mackenzie, who was highly touted only to have a rough go of it after Covid, would be way more ideal for a team looking just as much towards the future (like i said, he’s only 26), than some old retread clearly on borrowed time (cough Fleury).