I think the "why" is scouting and analytics driven. I suspect those departments have ranked pretty much every player in the league (or at least those that might get waived) and given them a score based on various parameters including metrics/stats, age/experience, contract status, "personality type" with respect to the Sabres nascent culture, etc. They probably also have a similar list for what the team needs/wants at any moment in time. Some players are rated "CLAIM" and some are rated "PASS" (which is why players like Vrana, for instance, didn't draw a second glance). So before the players are even waived the Sabres know which ones to target.