Bing is the most powerful search engine today, even surpassing Google in terms of search relevance and search results quality, however it loses billions of dollars a year.
Bing's market share is currently 14% but if you combine it with Yahoo (Bing currently powers Yahoo search results) the combined market share is around 30%.
To become a profitable business Bing has to increase its solo market share to 30% or more, and that market share must come from Google because all other minor search engines are not powering enough people to turn those 14% into 30%.
How long will it take? Estimations say that 3 or 4 years are enough if Bing continues to improve like it has been improving since 2009, but if Google increases its improvement speed and quality, Bing may be out of business is Microsoft considers that Bing is a loser in terms of money and human resources that could be used to empower other Microsoft products.
Most of the money spent on a search engine goes to the engineers and to the servers and the electricity spent every month. A search business is one of the most expensive businesses considering the amount of human resources necessary to keep the business expanding and improving because if a search engine improvement speed halts, competition starts to steal its market and profits go down.