I would say JW's commit suicide for the same reason other people commit suicide. They can not stand the emotional pain any more. All throughout my Adult life, from time to time I would think life was too much trouble.
And my stinking thinking would always lead back to the Kingdom Hall and Jehovah's Witnesses.
But then I would read about how to deal with suicidal thoughts and get through it.
Depression is a temporary thing, suicide is a permanent thing.
I suspect based on the number of books, I have read that there are a lot of ways to deal with suicidal thoughts so I will not list them here. Some may be too controversial for this crowd.
If you are too depressed to read a book and follow the directions then, you need to dial 911 and most likely they will put you on the road to overcoming your depression.
Overcoming depression and suicidal thoughts is kind of like dieting, lifting weights, learning a foreign language. The principles to recovery work if you work them.
It takes effort on the depressed ones part. It requires rebuilding your mind and then keeping it properly fueled.