Split links CAN come apart even when you don't want them to. Road or trail debris hits the link just right, a too-loose chain contacts something, or a thin metal bit fractures.
On a lower-powered bike, or at lower speeds, it's not as likely. But on a high-powered bike with the chain under bigger loads ...
A split link CAN come apart, and many of us have had it happen. A riveted link CAN'T come apart unless you press it apart.
Simple as that, I think.