Long and tall with no acetol (sound it out) caused this to happen. Without bashing any part of the Shorthorn breed (same thing works for Angus and Herefords), it developed when larger frame was the craze. Long, tall, light-muscled critters were winning the ribbons and being promoted as "modern" while muscle was often overlooked.
I remember one breeder remarking that it was good that a certain bull had large ears, so that he was visible when viewed from behind. During that time the breeding selections (and show ring placings) were all about going for the largest frame score. Unfortunately muscle was not the only thing lost in the shuffle. Sometimes correctness, disposition, fleshing ability, etc. also were sacrificed in the race to the top.
"WE HAVE MET THE ENEMY AND HE IS US.” Pogo