Bismillahir Rahmanir Rahim.
Assalamu 'alaikum wa rahmatullahi wa barakatuh.
Download requires connectivity with Intnernet and files are to be stored from our servers to the users mobile phone. The entire Quran is very large and while downloading this over an Internet connection can create unforseen issues. For example the phone running out of memory or disconnectivity of Internet or overuse of mobile data.
This is why we provide the option to download each surah individually.
The ideal use of our application is as follows:
Our application is designed to download when required - by long tapping on the ayah and selecting PLAY FROM HERE. Or by downloading surah by surah (see http://qamarapps.freshdesk.com/solution/articles/1000219898-downloading-audio )
Jazakallah khair for using our apps. May Allah reward you for your reading/learning of the Quran.