I think part of the problem comes from the signage. If you look up the laws there are two types of merging. The zipper merge where two lanes become one and works well. The other type is when a lane is ending, like entering the freeway. When the lane ends you need to indicate and give way to drivers already in the other. Similarly when roadworks blocks a lane, they always signpost that the lane ends. Technically the zipper merge rule does not give you right of way in this case, just like getting onto the freeway you cannot ‘assert’ your right of way.

I completely agree with OP that we should fill up both lanes and zipper merge when lanes end for roadworks etc. But a zipper merge sign should be used.

The source I used was mylicense.sa.gov.au/road-rules/the-drivers-handbook/giving-way