It's rather the other way around: Kojima was fed up with Konami's new management. The new CEO didn't really know anything about videogames or who Mr. Kojima was. He treated Mr. Kojima very disrespectfully, telling him that he wasn't really all that important to the Metal Gear franchise.
The new management is strictly business-focused. They believe that free-to-play mobile titles are the future. From a business standpoint, such reorientation may be the right thing to do. From a creative standpoint, this is unacceptable to someone like Mr. Kojima.
I don't know what you mean by "look at what was finally released of MGS5", either. The title was very well received by critics and sold very well, too - unlike Duke Nukem Forever.
The new management is strictly business-focused. They believe that free-to-play mobile titles are the future. From a business standpoint, such reorientation may be the right thing to do. From a creative standpoint, this is unacceptable to someone like Mr. Kojima.
I don't know what you mean by "look at what was finally released of MGS5", either. The title was very well received by critics and sold very well, too - unlike Duke Nukem Forever.