There isn't an "excuse" and there doesn't need to be one. He doesn't want to live there, and didn't want to live in Columbus either. It's not that complicated. Do you live in Winnipeg? If not, why? You could presumably move to Winnipeg right now and find a job in your field just like Dubois has, why do you live where you live and not Winnipeg? What's your excuse?
He didn't have control over who drafted him or where Columbus traded him, why should he be obligated to stay in Winnipeg? Dozens and dozens of players leave their teams as UFAs every year, he's just telling them upfront that he plans to do that next year so they can get something for him instead of losing him for nothing like the Islanders with Tavares.
That's a nice quote for the intro to a business book you'd buy at the airport, but I don't think that's actually true if what Dubois is doing is what makes him a "quitter" in your eyes.
Ryan O'Reilly quit on Colorado and stayed in the KHL after the lockout ended and then didn't sign with them, eventually signing an offer sheet with Calgary that the Avs matched. Then the Avs traded him to Buffalo, and a few years later he quit on them and wanted a trade while going in front of TV cameras talking about how he lost his love for the game. Then he got traded to St. Louis and won a Selke, Conn Smythe, and had a career year leading the Blues to their first ever Stanley Cup.
Matthew Tkachuk signed a bridge deal because he wouldn't commit long term, quit on Calgary with 1 year of RFA status remaining after a 100pt season, told the Flames he wouldn't sign with them, and then gave Calgary a list of 5 or 6 teams he would sign with. It is an identical situation to what Dubois is doing right now. Jack Eichel quit on the Sabres, demanded a trade, refused to get the surgery the Sabres' team doctors wanted, and stayed on the sidelines collecting a ten million dollar salary while making it harder for the Sabres to trade him. Now they're both key forwards for the two teams in the cup final. Sounds like quitters actually do win a fair amount!
Regardless, I have no idea how being upfront with a team that you don't want to sign with them a year later as a UFA is "quitting". Is every player that leaves their team as a UFA a quitter now?