Ps,
There is no evidence anywhere that he used this as a criterion. It was simply an observation that many of those big ballads had the elite as their subject. However, the more likely scenario, as presented by many scholars I have read, is that the earlier ballads were most likely written initially by members of the elite households (I hesitate to use the word minstrel because of what it conjures up). Some were undoubtedly written by the early broadside writers. In fact we even know some of their names.

Whilst it is possible, even likely, that a few of the ballads were written by the elite to amuse themselves (they certainly had the time), why bother when you pay someone to do it for you? A couple of the Child Ballads have been attributed to James VI but I don't think it's proven.