Because investment from all over the world is flooding here as one of the last stable markets. Look around the world. There's a lot less sensible choices these days.
You say countries under healthy 2% - 3% inflation.. Ed just crossed a new dynamic in the Treasury market but he seems not interested except stock rally
2 wars in the world
1 in the making right in US backyard
A president fast losing support in his own party
But SnP 5400 doesnt look aggressive