they set up contracts with premises not to let competitors in the buildings, those contracts have been made illegal, but they still existhow are you going to know they exist to eradicate them.

Sure but a co-op wouldn't need to be in a shopping centre next door to colesworth.

Plus high rents that are killing for profit businesses

This effects everyone, and isn't a reason why co-ops aren't common.

that combined with Coles + ww buying power

This is the most credible reason that most people are proposing. IGA stores share a purchasing and distribution network to mitigate this disadvantage as much as possible. I don't know much about that.

They also sign contracts with producers that don't allow them to sell to anyone else.

True. The flip side of this is that smaller local producers could work with a co-op.