Wolf, precisely because of your questions, I named it interesting. However, it isn’t exactly so. Pain and bereavement are two different things. When parents lose a child, they comfort themselves with the education they gave him/her. The deprive themselves with the care they gave him, and they hear all the Chizuk and good deeds about their child. On the other hand, a person who committed suicide usually doesn’t have this. In addition to their pain, they are usually ashamed and cannot face visitors. They cannot comfort themselves with the notion that they cared enough about the individual and just want to turn the page. Eliminating the Shiva practice makes it easier for them to disguise their suffering and pain.
Note: Even with the pain of losing a loved one (especially a child), there is still the “Gezeira Al Halev SheTishtakech Min HaBeis” – the pain lessens over time, whereas the consciousness of having a suicide individual in the family stays forever.