Some metro areas have a plethora of choices, while others are really lacking. There doesn't seem to be any major trends, except that longer bridges tend to be more well-known... and maybe the more significant the river, the better the bridges?
Compare Pittsburgh, PA (which has three historically significant rivers and a lot of great bridges), to Columbus, OH (which has two little-known and largely insignificant rivers, the Scioto and the Olentangy, and no famous bridges). Night and day.