Why is Google losing share of search market?

The answer is complicated but mainly over 2 years, Google search has been perceived as lacking in innovation. Also previously, people would search for any content on Google, now people tend to use Facebook for discovering new content through friends.
Also Twitter has become increasingly popular medium to keep in touch with current events and news.
This is where people might be flocking away from Google.

Bing is not really a threat…

The obvious point to assume is that if Google falls, Bing rises. That is not necessarily true as Microsoft is still pushing great amount of money into its internet services including search but are not making profits of it.
This means, Google is still the only profitable search engine around and as long as that is happening, Google will still rule the internet.