I think because most can not shoo the heavier recoiling round as well as the light 40. Same w/ 45acp+P. The extra recoil slows most, including me, down for multiple shots. The object is to hit w/ every shot & extra recoil slows you down in order to get those hits. JMO, & I regularly shoot 44mags & heavy 45colts, but I know I am slower w/ followup shots when going much beyond std 45acp especially in a lt.wt. 1911 or G36.
"Given adequate penetration, a larger diameter bullet will have an edge in wounding effectiveness. It will damage a blood vessel the smaller projectile barely misses. The larger permanent cavity may lead to faster blood loss. Although such an edge clearly exists, its significance cannot be quantified".