According to TCGPlayer.com, the average selling price has continued to increase recently, which means despite the increased supply, demand is increasing faster
Multiple cards in March of the Machine also refer to being transformed, making it a quasi-typal synergy
Usually the Turn 4 attack with two Construct tokens is lethal by itself, discounting the other creatures and payoff you draw, and this forces your combo opponent to interact or to go for the combo without having enough time to set up
Subsequently, Wizards chose to frame this ban as a little shakeup. While this was arguably the right thing to do, it was a deeply controversial choice that threatened the integrity of future bans
(By the way, cards with cheaper alternate play costs like Avatar of Fury will still trigger Kalemne.) There are multiple cards from Oath of the Gatewatch that really seem useful for Commander, generally, and Kalemne, specifically