Keeping salaries secret has been a huge tool wielded by hiring managers and HR in order to suppress salaries for a very long time, especially with the way engineers are typically pigeon holed in to broad titles. I don't see that changing any time soon, as much as I'd like too. It'd solve a number of problems for our profession if that were so. I'd be interested to see what the differences are from the initial offer when reaching out and what the official offer is if a candidate accepts.
I'm guessing most businesses that use this platform have figured out the optimal number to get responses from recruiting emails and then used any leverage they can get in order to discount the engineers skills and experiences in order to get them in to a lower salary. Unfortunately engineers are notoriously bad negotiators and we start to buy in to their arguments and end up accepting bad deals and we don't realize it.
But, this is definitely a step in the right direction.