This practice should be illegal.

This is usually called bait and switch, but your point still stands.

I think the GP's point is that if you give the companies the opportunity to do that earlier, instead of only later, you get to save a lot of time dealing with the honest low-ballers.

There's nothing you can do about the dishonest ones.

It really should be against some kind of employment standards to do this sort of bait and switch

There are apparently some new regulations in Canada to protect job seekers from this, but it's not a clean line in the sand. It seems like companies won't likely be held accountable unless it is a pattern of hiring like this, but how do people establish a pattern when most people still won't discuss salaries?

Most companies want the new joinees to be satisfied, and if the reason is "we don't have budget" that might be acceptable. But if the reason is "we are lowballing you specifically because we can" that would just create spite in candidates mind and the company has to pay the price for the process if a candidate dropped off or joined temporarily while looking elsewhere.