This page is for an offline DESKTOP/LAPTOP version, not mobile. To vote for a mobile app, see: https://noteflight.uservoice.com/forums/4962-tell-us-your-thoughts/suggestions/4327326-ios-and-android-apps-instead-of-accessing-throughStephen commented
I think that a good reason to make an offline version would be for performance. At the moment, Noteflight relies heavily on internet connection, and even with top speed internet connection, it is still incredibly laggy. It works brilliantly with ensembles of up to 10-12 instruments, but as soon as you start arranging for a 16 piece Big Band, Concert Band or Symphonic Orchestra it is almost impossible to get any more than a few changes/inputs into the score before it lags out and often crashes.
This needs to be fixed if Noteflight is to remain my notation software of choice.