Compare simple AM modulated LOC and GS transmitters with antennas anchored in concrete to triangulating from a bunch of tiny transmitters about 11,000 miles away.
GPS can plot your position with reference to the center of the earth, and then a model of the earth's surface tells you where you are. Did I mention software?
"Once proven, software never fails." Yeh, right. Think of the mountains of software to just show present position.
ILS is elegant and simple.
GB