It's a prerequisite requirement on promotions. Any company that wants to promote their sales needs to do so in accordance with relevant consumer law, which means ensuring they have available stock for the promotion before starting it.

It's not as if retailers in this environment just say "well, it's a potential risk for us to promote something if we don't actually have enough stock to consistently offer it at that price, so we just won't promote anything". Of course, promotions are beneficial for sales either way, so they just make sure they have enough stock before doing the promotion. The requirement doesn't stop them from running effective sales promotion without intent to exploit.

They aren't at some risk of blank cheque liability resulting from this, they just have a legal responsibility to ensure appropriate resolution case-by-case. Often that just means offering a raincheck, so the outcome isn't even different in Canada. But there's a difference where in Aus the raincheck solution is secured by consumer protections, rather than the retail company policy.

Overall it's not hugely impactful legislation, just the company bears the consequence of their own mistakes in the unintentional bait advertising circumstance and whaddaya know, bait advertising is mysteriously not a problem anymore in pretty much all western countries outside NA