That's not entirely true. Greens are much more active in Britain for example than Canada despite using almost precisely the same electoral system.

A significant part of why I think they're so weak in Canada is they're not as coherent in their message. Their platform and base is actually much more conservative than a lot of European Green parties, which turns off the more progressive left environmentalists, and leaves them struggling for more conservationist moderates, who are kind of a dying breed.