According to Steve Propes and Jim Dawson' book "45 rpm- The Heroes & Villains........" , it was a matter of convenience and to minimize stress on the records. Record changers which made it possible to stack discs on top of each other were popular. They found out that with 78's, that the records were getting chipped or cracked. So, to minimize damage on the 45's, engineers found out that a large center hole reduced friction and other stresses from record changers.