Quoting: PrisonMike
In context Reimer was the starter on a team that was REALLY struggling with one playoff appearence. He'd be the backup here.
So you're saying they should have went with Murray + Reimer instead?
Also, I made a mistake earlier, Murray was acquired after the July 11th 5pm deadline for qualifying RFAs so they knew that Samsonov could have been an option but he may not have chosen them. All the other "1A" options were basically gone Campbell wasn't taking a discount, Georgiev (traded July 7), and Husso (July 8). I don't think they saw Reimer as a 1A option.
Samsonov is definitely a better option to go with over Reimer just because he's younger than Murray, while Reimer is older. So, even if Murray+Reimer made a good tandem, the Leafs can assume from now that they will need a new tandem in 2 years (assuming Reimer extends). Samsonov has the potential to be the goalie for the next 5 years, like Andersen was and perhaps they can get him at the 4m deal that they seem to want so bad (I think they will have to bridge him to a 3mx2, and then he's going to get paid here or elsewhere).
If you meant they could have traded for Reimer after Murray's injury, then the reason they didn't yet is that there is no rush since Murray was allowing them to keep a player that they would otherwise have to move (that's before Muzzin was injured too).