It's just not the time for her. I respect her deeply and thought she was great in the debate, and she did a great job last time Trump was in power.
I just think she couldn't win the next fight (the general election), and frankly I think a PM who Trump completely loathes would become his punching bag instead of his foil. Freeland could take a punch for sure -- don't mean to imply she's weak, but I think it wouldn't help.
I worry about Carney not being an outspoken and charismatic leader against Trump. Between Pollievre and Trump I think he's going to get dumped on, but I trust that he won't care because he'll be heads down enough on the technical sides of leadership it doesn't matter. We're already united, he can be a general and tactician.