When we ask someone for a favor, we often assume that they expect something in return as soon as possible. (While technically, a favor is something provided out of goodwill, the business connotation has evolved into something else.)
To ask for a referral is not to risk a relationship or a friendship, as some authors claim. If we erroneously believe "referrals are a favor/risk," then we would never ask for referrals. Or we'd ask in such a meaningless way, that we might as well not ask in the first place.