Unions in general need to do a lot more to get the general public on their side. There's a reason why union participation is so low in North America(a lot of it due to shitty government policy), but for a long time there has been a widely held view that unions are no longer necessary.
I work in a union shop, and I am generally pro-union. But when I encounter the usual anti-union sentiments among the non-union public, I can't really argue against them. Unions do foster and protect lazy individuals who take advantage of management's unwillingness to take the union to arbitration or whatever other cumbersome processes are involved. I've seen it, and I can't say that I haven't benefited from this either. It's great, honestly, and it would be really nice to know that everybody could work in an environment where they felt somewhat secure(even though layoffs have felt imminent for what feels like more than a decade now).
In the case of the postal service strike, the media has been pointing to a growing backlog of packages caused by the rotating strikes. CUPW have stated on a few occasions that no backlogs exist. Logically, this means they are getting more work done in less time. So what exactly are they complaining about? Whether the backlog exists or not, painting your service as underworked is probably not going to do anything positive for your claim that you aren't being treated fairly or that you are being pushed to injury.
I don't really know what my point is, other than if the PCs and Liberals felt any kind of insurmountable public pressure against intervening on behalf of Canada Post(and, by extension, Canadian business and consumers), they likely would not have stepped in. But they know that the opposition to moves like this is usually forgotten when business returns to normal, and likely seen positively when people are no longer inconvenienced. Labour need to figure out how to make themselves more appealing to people who aren't involved in the labour movement.
I struggle with my own thoughts on this subject, because I don't like the idea of government impeding the bargaining process. Especially since it seems to promote the idea that collective bargaining is just a boutique concept that can be tossed aside at the slightest inconvenience. But I've had issues with my own union's leadership and how they are stuck in the past(old white dudes, of course), and completely reactionary. They also backed Donald Trump thinking he was going to be great for Canadian workers. Hah.