Soldier Field isn't 100 years old. It's 19. The facade surrounding the building is 100 years old.
Lambeau Field had an inflation adjusted 455 million dollar renovation in 2001 and another 150 million dollar reno in 2013.
And you are right, our stadium isn't in the group of historical stadia, nor should it be. It's old, and not everything old is historical.
And FWIW, Cleveland moved because the city jerked Art Modell around about a stadium for a LONG time.