TL;DR they think he should look at electoral reform again

A huge wedge of the liberal voter base were disenfranchised when Trudeau promised electoral reform, practically guaranteed it, and then just announced they weren't going to do it but don't worry here's legal weed. Many of them were youth voting for the first time, and that betrayal set the tone. If he set it in motion before the election, is it possible they'd recapture at least some of that base? Sure. Would I vote for him? Not a chance.

Wow imagine if he just actually kept his campaign promise

Pffft, Trudeau would rather set himself on fire than enact electoral reform.

FPTP is too critical to Canadian neoliberalism in that it prevents coalitions (which would encourage compromise and diversity of opinion) and allows the major parties to force their will.

Edit: Do I have to explicitly state that neoliberalism is bad? Lol. Obviously electoral reform is needed - but there's clearly a vested interest among politicians in it not happening.