With many difficult decisions to make after training camp, having to assess the salary cap and become compliant, the Maple Leafs decided to keep Denis Malgin up over the aforementioned Robertson for the sole reason that one requires waivers and the other doesn't. Something that Sheldon Keefe said was "just the reality of the situation".
Malgin, 25, has played in 192 games over his NHL career - all but 8 with the Florida Panthers - with 28 goals and 60 points in that span. Nothing all too spectacular, though he did post exceptional numbers in the Swiss League in back-to-back seasons in 2020-21 and 2021-22, posting 94 points in 93 games and improving all of the details of his game before coming back over to the NHL. Apparently, it worked.
Robertson, the Leafs' second round pick from 2019, is set to join the Leafs at some point this season after an exceptional training camp, tying with Malgin for the Leafs' preseason scoring lead with 8 points. His fast-paced, highly-skilled game is going to compliment the rest of the offense very well. He'll just have to continue to be patient and wait for his opportunity this season.