A question about ESL teaching?

I am a trained and an experienced teacher to teach English. I have worked with native and non native English teachers and have felt that non native people have a better command of English as compared to the native ones. My concern is then why at the time of recruitment, non native speakers are not considered for the opportunities, when they are fully equipped with proper education and experience? just take a look at various job boards...native speakers only, no experience or training required...