• Candy Crush on smartphone

Candy Crush on smartphone (Photo : Reuters )

The top mobile games of 2015 including Candy Crush and Clash of Clans were also the leading titles three years ago, showing that a few smartphone apps are dominating the industry. Time spent gaming on mobile devices has dropped over 50 percent since last year, due to rises in in-app purchases such as cheats, and causing "esports" watching to increase.

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Flurry is Yahoo's analytics firm. It has reported that time spent gaming on smartphones has dropped from 32 percent last year, to just 15 percent  in 2015. The number of minutes played tumbled  from 52 minutes daily to 33 minutes.

Simon Khalaf is a Yahoo senior vice president. He noted in a blog post that there have been no major new mobile game hits in about 6 to 9 months. Titles such as Game of War, Clash of Clans, and Candy Crush still top the smartphone charts.

The industry's leading mobile game developers have secured a large portion of the market share. Then they double-down by boosting their marketing.

One example is the hit game Clash of Clans. Since November 2012 it has not dropped out of the United States' top 5 highest-earning iPhone games, according to Venture Beat.  

Other factors have caused the market to level out. Due to the success of the top-grossing games, other companies develop similar ones. Besides that, Khalaf explained that many gamers are spending money to advance in video games, instead of grinding through them. This results in less gameplay.

These purchases are known as "micro transactions," according to CNBC. The multibillion-dollar industry is based on smartphone apps that are free to download, but cost real money to advance in tough game levels.

Such in-app purchases helped to fuel the Apple App Store's receipts for July totaling a record $1.7 billion. Gamers are then spending their extra free time to watch other people play games.

Such "esports" have grown in popularity among millennials. Many are spending oodles of time watching experts play Minecraft and other video games on platforms such as YouTube and Twitch.