I'm so sorry for your loss. Losing a loved one to suicide is traumatic. You wrote that you'd want someone to tell you why people do that. I don't know as there is a simple answer to that. Whole books have been written on the subject. And research on this topic is ongoing.

One thing that occurs is that the suicidal person's focus tends to become more-&-more narrow to the point where s/he loses the ability to see any other options beside suicide. There is something going on in their lives that weighs heavily on them. But they can't see any other ways of resolving the problem except to end their lives... even though there are always alternatives.

You wrote that you do everything you can to talk about your uncle's suicide. That's a very good thing. Talking about what he did, & how you feel about it, is really important. I send hugs your way with the hope that you will be able to find deep peace in your life.