Because when you list the entire band, people naturally will demand being at the top of the band, of be insulted if you offer them salary at the bottom of the band, even if it is warranted.
IME it's usually because they'd be prepared to accept less not because they're actually less productive.
So? That sounds like the applicant's problem if they do not want to accept the buyer's offer.
Just list the lower end of the band as 20% less than the actual lowest offers. Does the law prevent that?