To date, mobile devices that use Android have not been powerful enough or had big enough screens to run Audacity.
As new, more powerful devices become available it may
become viable for software developers to port Audacity to Android, but for the foreseeable future this is unlikely to happen as many of the building blocks that Audacity requires are not available for Android. For example, Audacity is a WxWidgets
application, but WxWidgets is not available for Android. Creating a version of Audacity without WxWidgets would require a total rewrite, so in effect it wouldn't be Audacity.