Part of the problem with the Hetar Meah Rabbanim was in the time of Rabbenu Gershom it was quite difficult to to and I belive there is also the requirement of the 100 Rabbanim being from 3 different continents, so in his day it really was a last option
Unfortunatly today because of the smaller world we live in one can easily abuse this, You can get 50 Kollel guys to sign in Brookkyn or Lakewood, fed ex the document to England and get a few to sign there and fed ex the document to Israel and get the rest there. it can be done in less than a week. In Rabbenu Gershon’s time it tooks months or years to do