I'm guessing it's for the same reason that The Harbor expasion for Machi Koro which changed the game to this style did it. To make it so you can't just tunnel vision one working strategy every game.
Exactly. And to lower the AP of players looking at 22+ different cards.
And because meds and buildings are vital for many strategies to become even possible, there is a set amount of medics and engineers at the start of the game equal to number of players, so each player has at least a chance to get one of each, even if their unlucky to find meds in the junkyard or if any engineers or tinkers don't show up.