While I agree that Chrystia Freeland would be a far better pick than Trudeau as PM, I can't see any reason why Trudeau would willingly give up his PM seat right now.
Yes, his name has been dragged through the mud, but as Mike was saying, the Conservatives have consistently shown that they are in no position to govern.
So if Trudeau can still enjoy a safe margin of winning, why would he willingly step down on his own? And who can pressure him into stepping down when he could still comfortably take the next win at the federal election?
If the Cons were putting up a tight race, then I can see how the Liberal Party would consider / force Trudeau to step down, and let Freeland take up the party banner. But that is not what we are seeing right now.