Because the 'native' UI is ... HTML/CSS/JS. There is no non-HTML 'native' UI on webOS.
Don't want to implement RSA in javascript? Create a 'hybrid' webOS app using a C lib, but 'native' HTML UI.
The 'native' Mojo or Enyo frameworks may not be as rich as UIKit, but the web UI ecosystem you can leverage to extend them is massive, and the source for both is all there for you to read and extend.
