Commonly proposed reasons I've seen mostly involve conscientiousness around impact on their body and setting. For the most stereotypical two methods: a gunshot to the head leaves a mess and means you're going to need a closed casket, while the mess from a slit wrist in a bathtub can be washed down the drain, and easily hidden while still having an open casket. But it's harder to "succeed" with a slit wrist in a bathtub, and it takes longer, giving more time to be found or to change your mind.