lol you replied to a very old thread, but the reason is because them the 1300 person will lose rating making it not fair.
But.. They will learn to use new strategies to improve.
That's how i improved. i lost, asked questions and tried different things which all helped me understand better.
Like with begginners for example, if you don't give them a tutorial or help they will fail. give them a tutorial and they will know the BASICS. Playing with the masters is very beneficial IMO.
But i do partly agree with you about the lesser players losing rating to someone they would never have been able to beat at their level, it's unfair and the loss of rating should be significantly lowered if you lose to someone at least 100 above your current rating