What's the cause of the iPhone/Flash controversy?
The reason for the iPhone/Flash controversy is Apple CEO Steve Jobs's decision to not support Flash on the iPhone [1]. The issues with Flash are the battery drain and performance issues [4]. HTML5 has become the preferred interactive medium because of its performance over Flash [2]. Flash is being phased out because of its limitations, and websites are now designed to function without it [3].
The iPhone controversy is due to the fact that when the iPhone was first released, Apple's CEO Steve Jobs made the decision to not support Flash on the iPhone [1][2][3]. Although Flash was popular at the time, Steve Jobs reportedly believed that HTML5 was a better solution [1][3]. This decision, followed by the iPhone's sudden popularity, prompted the tech world to produce web content that was compatible with the iPhone and iPad without needing Flash Player [1]. 

Another large contribution to the decline in Flash Player is the rise of HTML5 support and overall performance. HTML5 video support was introduced to Safari 4 (2008), Firefox 3.5 (2009) and Internet Explorer 9 (2011), thus allowing developers to take note of the increased performance over Flash Player [1].