A major issue with stadiums getting smaller, is that the new ballparks are all baseball only stadiums. The stadiums built in the ‘60s and early ‘70s were almost all built for both baseball and football. The seating arrangements, sightlines, etc. are different for a football only stadium and a baseball only stadium. Building stadiums to accommodate both sports meant the stadiums were not ideal for either.
Shea Stadium...in either original configuration, baseball or football, all seats faced center of the field. Rolling field box sections and temporary stands added for football accomplished that.