Why Aren't Baseball Fields Standardized?

The main reason for this is that there is no designation for the authorized size of an outfield. In the official rules for Major League Baseball, it is stated that the outfield fence should be at least 250 feet from home plate. A distance of 325 feet or more along the foul lines and 400 feet or more to center field has since become mandatory for any new stadiums. As such, professional fields are all a little different. Even more significant is the fact that those rules only apply to MLB; a field designed for youth baseball or even college baseball is likely to have somewhat (or substantially) shorter fences.