Firstly it gives Poilievre an honest opportunity to contribute. People want to see everyone working together, so by letting Poilievre in right away he's giving him a chance to temper the rhetoric and get work done. And if he doesn't temper the rhetoric, it's likely to work in Carney's favour. If he's seen as obstructing, it will not look good for him. It seems like a win-win-win... It looks like fair dealing, if Poilievre comes to the table honestly it works for Carney, if he doesn't it works for Carney as well. It's good politics that is both strategic in the way it encourages good cooperation and has good optics around fairness.
Secondly, the elephant in the room is the separation nonsense. Poilievre is running for a seat in the heart of separatist country, and with the separation rhetoric ramping up, better to have Poilievre - who is ideologically tied to Smith and will be representing Alberta - in the public eye as soon as possible, so he can wear this garbage. After all, Smith seems to be adept at causing no end of hassle for Poilievre. Best to put him front and centre as soon as possible so he is forced to respond to it.
Thanks for letting me know, those guys are solid, glad to hear they did this.