They avoid currency risk and hedging cost if they get secure returns by investing in us govt bonds...besides interest rate are rising and inflation outlook is good....Trump doesn't like fed tightening, trade wars are also posing threats and uncertainty...
Market have in the past always hated uncertainty and show their ugly side by discounting the uncertainty well ahead of events....
There was a time when Indian markets we're delinked and decouple from world markets...it was 2007 end to 2008 start period....u all know what happened later period