Why was Glacier National Park preserved as a National Park?

Well said M.Q. !!

After the Great Northern Railroad placed a line at Marias Pass over the Continental Divide in 1891, while promoting the the route as a tourist destination, they also lobbied Congress and the president to protect and preserve the area. With further lobbying from the Boone and Crockett Club, President Taft declared it a National Park in 1910.

Because of its Natural, historic, and cultural standing within the U.S. of A - it was a native American sacred lands prior to it becoming a reservation. I visited it last summer, it is very a very special place. Go visit!!