Who's saying he isn't? At this point they're trying anything.
But I'll grant that Harper is, at least, not a guy who has spent the last ten years regurgitating whatever bile comes out of Trump's mouth. At this point Pollievre is completely toxic to older voters because he's seen as a reflection of the US politics that lead to our closest ally declaring us an enemy. Harper should be completely toxic, but given time people tend to forget the bad that someone did, and you're left with just the fact that he at least doesn't come off like a whiny teen on 4Chan yelling about "THE WOKE RADICAL LEFT" or whatever dog whistle for "queer people" they're using now.