I know very little about Canadian politics and culture, but this is hardly a Canadian phenomenon. Rather this is an emergent behavior of internet and social media, that certain types of debate end in partisan convergence much more efficiently than they used to.

The observations about the form of bias in question, as well as the observation about (lack of) dissent within the party, are really just minor details of a wider picture.

The root cause is that hyper connectedness has reduced cultural and intellectual diversity among the vast majority. I don't say that as a positive or negative, just as a fact. By "cultural and intellectual diversity", I mean that the more a particular topic is featured on social media, the narrower of a spread the opinions on that topic become. (Intellectual diversity in the sense of what topics are discussed has exploded, however. I'm part of a massive online group dedicated to discussing changes in zoning and public transit. Imagine that 30 years ago.)

This goes beyond politics too. I could write an essay about how games like MMORPGs are fundamentally different now that there's hyperconnected communities that distribute high quality information on playing optimally, and how game design has in turn responded to this. Effective use of reddit or discord or a wiki has essentially merged as part of the gameplay now for a very large percentage of users. The hyperconnected social internet fundamentally changed how we interact with ideas, from gaming to politics.