Here's a few things you probably don't know:
1. Interprovincial trucking is subject to federal regulation (provincial/local trucking is not, and is also only a relatively small part of the supply chain problem). There are many issues for such interprovincial trucking associations to navigate with the Federal government. They will pick and choose which battles they wish to fight publicly. Most of these negotiations take place behind closed doors. The fact that Associations don't want to address their issues by way of organized protest does not mean they are offside with the points the truckers are making.
2. Independent truckers (which a large percentage of long haul truckers are) are not represented by the Associations which have been asked for comment and, in truth, are their competitors.
3. Trucking companies care about profits. Individual truckers care about their own personal earnings, and just about equally, about the freedom their lifestyle affords them. You can't assume those interests are perfectly aligned. Perhaps the trucking companies are happy with reduced tonnage but at higher hauling rates? That business model, however, doesn't put more money into the pockets of truckers.