I have over 100 articles on ehow and only earn $25-30 a month
. They cut about 6 of my articles but whatever. In general some articles will earn nothing and some will be no particular persons highest earner.
SEO plays a part, but so does interest in the subject of the article and whether they have the ads matching what you wrote about. I'm nervous to write for them now because they've become a lot more strict about their rules/format.