I actually sent a mail to youtube asking them not to give me some form mail reply and to honestly tell me what the reason for refusal of videos it. I have to honestly say I think they have some kind of internal quota. They refuse videos based on number of monitized ones in your account vs non monetized ones. It has nothing to do with your content because their decisions are so all over the place that there is no rhyme or reason in fact I bet you could repackage the same video and have it refused sometimes and accepted other times. I was thinking of using my channel to experiment and then posting the results publicly on some very busy places. I think my results would be that they are just filling a quota and somedays they come by you and your ration of 1:10 or whatever has dropped and so they flip a switch and let you through.
There are a few reasons I say this most royalty free stuff even if it says "non-commercial" that non commerical does not extend to ads just a little tidbit of info. The non-commerical means that you can't sell it on a disk or package it with something your selling outright. It also extends to using the royalty free stuff in things like actualy commercial advertisements. The non commercial attribution generally is okay for what we do with it . However youtube is doing something bizarre and I am sure there is some reason unbenownst to us all. At the bottom of it though is the fact that well half the work is being done by computers and not people.
I doubt they will ever answer my email because it means I am asking them to stop cutting and pasting and give me a logical answer