Why in case of a stab (especially if the person stabbed is significantly tall) - its the belly which usually gets wounded?
I (21f) am a pretty short (5’2") fencer (HEMA, rapier), and I often get advice to target a tall opponent’s belly with my rapier. Also I’ve attended a self-defense class, and the instructor gave me advice to go for the abdomen of a tall attacker, if I have a pocket knife in my hand.
The Human Body “center of mass” is at or above the hips, it’s where the majority of weight is and all movement is around this point: standing is holding this point up, walking is pushing this point from behind it, etc. It’s generally a slower target than extremities and upper body.