This task of Mike's suicide is called causal cycle, as the name implies. At the beginning of the game, in order to get rid of this wandering and plundering life, Mike cooperated with FIB agent Dave to "defect" the robbery team, resulting in the killing of hillbilly and Brad and Trevor's disappearance.

Then, as you can see, Trevor kept remembering Mike's death because of his own fault, and met Mike again in Los Angeles. Then, as the plot is unlocked, he gradually discovers that Mike was deeply cheated and betrayed in the robbery nine years ago? So I feel very angry.

When Mike saw that Franklin didn't kill Trevor like a madman, but found him, I estimated that Mike's heart was as causal as the name of this task. The same betrayal, Mike betrayed the team and cheated Trevor and Brad; Franklin betrayed Mike and came to him with a gun, so Mike probably thought it was retribution for what he did nine years ago, and God knows he was unhappy. Therefore, psychological despair and collapse, rather than dying under Franklin's gun and in the name of punishment, is better to kill yourself, redeem yourself and gain peace of mind.