Because Dubas did what every single GM would do, and gave their young, cheap, home-grown, Calder-Cup winning, AHL goaltender of the year a chance at backup, instead of losing him to save a 35+ journeyman waiver claim that was going to hit UFA in a year, who is not the god that people treat him as because of his one fluke season in 2017-2018.
Because Ceci was already locked into either a contract or an arbitration hearing by Ottawa, and because Ceci was a better player and better fit than 38 year old Hainsey, with the potential for more.