Imagining a 'systematic' left bias is pretty naïve
What else would you call it? Just looking at the polling aggregates, every poll since about 2014 has said Labor victory. The only two exceptions are both elections. That's not one poll but about 50.
At that point we can estimate a (at least in the Australian context, of about a 1-2 percent systematic error in favor of Labor lean.
Given a sample without systematic bias, we'd expect 25 +/- 8, so there would be no more than 37 polls. The chance of all 50 being Labor without systematic bias is, what, 3.5 standard deviations there about? A tenth of a percent or so.
The problem with systematic biases is that they exist until they suddenly don't. For all we know, polls might overreact and underestimate Labor next time. Or keep overestimating them. Or be spot on.
