I wonder how looks other than height affect the job. You probably don’t want your bridesmaids to be prettier than you, but you also want them to look good for photos. That’s a fine line for most of the population.
In my experience, the entire point of bridesmaids is that they are your friends, sharing your "special day". The photos exist to document that you were, briefly, the top of the social heap and the center of attention. It wouldn't be meaningful to hire non-friends.
Which isn't to say it doesn't happen, of course. And since TFA says that the get 10-20 "inquiries" per day, it may just be that with > 1 billion people there's always somebody doing anything. In which case it's probably hard to draw any patterns about what people want, since they're so far off the end of the bell curve.