>> It does not seem to apply to employees wanting to move from one to the other, or does it?
Yes it does.
You work for A, but think the grass is greener over at B. You approach B, and may even be applying for a specific advertised job.
Normal practice would be that B would look at your experience etc, and if you meet the criteria for the job, are better than the other candidates, etc then they may make an offer based on what they a) think you are worth to them, and b) what they think you'll go to them for. If there is a demand for people with your skills then pay goes up - laws of supply and demand. Even if you don't move, the fact that other employers are prepared to offer more pay means that your current employer (A) may well increase your pay so at to avoid you leaving.
With this illegal agreement in place, something different happens.
When you apply for job at B, B has agreed with A that :
a) they will tell A that you've applied for a job with B, so your current employer knows what job(s) you are applying for.
b) they won't offer you any more than you are on now, so you can't change jobs to get more money. Suddenly the laws of supply and demand no longer apply, and only people from outside "the group" can benefit from having in demand skills that result in higher pay.
So two of the three agreement points DO directly affect someone attempting to apply for another job in the industry. The only point that wouldn't apply in this case would be the one that says B won't contact employees of A and try to entice them away.
The direct and foreseeable result of this agreement is to artificially hold down pay to the detriment of employees and benefit of the employers - that's why the big 6 entered into it, and when they were found out, have been hit hard for it. It's also why, having been found guilty, the employers are now facing claims from employees wanting to make up some of the lost earnings.