This is because of the locked tokens to certain classes. A 25man can get away with it since out of merely big roster numbers they usually even out relatively OK. A 10man though is easy to have 2 on a token, or 1 on a token or 5 or even 6 members on a single token (if it's the big token especially).
So, when you have valor, at least you're 'fighting' over 1 or 2 tokens max, with this, you're going to be fighting with people for at least 4 tokens.
Now, this wouldn't happen if a token could go to any class or if Blizzard became responsible and started being less random, and gave drops according to what it sees online at the time.
Or then if it's unfixable, put back some tokens on valor.