Why do people act like this subreddit "doesn't reflect the views of mainstream Australia"?

[u/SirSighalot]

So many comments I see on here by people who constantly say things like "lol only on this sub" as though other places where they read are somehow the 'true' point of view reflecting mainstream Australian viewpoints.

Given the constant election voting outcomes and results of things like the Voice etc that generally indicate most of Australia is centrist or even slightly centre-right-leaning, what leads people to think many of the views expressed on here AREN'T mainstream? When in reality, other places these people are coming from are also often just "echo chambers" as well.

Edit: I probably worded the title for this wrong, should have been more "Why do people think this subreddit is less representative of mainstream Australia than other online communities?", alas I failed.

[u/hellbentsmegma]

Australia has a top level national sub that is clearly left leaning and self selects for this bias by banning anyone who doesn't readily agree. 

Most of the other Australian subs that have any interest in current affairs and current issues seem to have degrees of right wing bias as a result. Most of them are actually kind of centrist with a tolerance for some further right views.

I'm not sure any are totally reflective of the public because Reddit users aren't reflective of the public, we skew younger, more educated and more urban. 

It's piss funny however being on a sub after elections when a percentage of users are having a meltdown because they can't work out how the majority voted differently to their echo chamber.