I realize with many voice commands there is the option to select programs from which to do this, Google calendar is the only one I am able to. If Google calendar is disabled, it says "no appropriate program to do this with" (or whatever that error message is, basically saying there's nothing to complete the command). And when Google calendar is enabled, there is no choose-able menu with apps, like how if you told Google now to play a song you could choose from Google play, Spotify, etc. There is no choice in default apps for me with calendar events, only Google calendar.