The question “Why did Yama Buddha committed suicide?” is still unanswered (at least, officially). The official report – post mortem report says that Anil Adhikari, Yama Buddha, had committed suicide. Although there was injuries in his jaws and he had taken some wine – there were no signs of anybody doing any foul play. The police has done the investigation and has rule out any issues.
But, a lot of conspiracy theories are going around. I think the story presented in the following video makes the most sense.