Against a serious aggressor, it will take serious and possibly fatal harm to halt the attack. Whether it's a face full of pepper spray, a stun gun, a baton, a machete, or a gun, the idea is to make your assailant feel crippling pain or to cause enough damage to cripple or kill them.

Perhaps one day we will have rapid-firing, multi-shot weapons that cause unconsciousness without causing physical damage, such as a phaser set on "heavy stun" in Star Trek. I can even see a future where such phasers are commonplace and widely owned, but, unlike perhaps military versions, there is no "kill" setting. Law enforcement and the general public could be limited to stun-only phasers (although according to the ST:TNG technical manual, heavy stun lasts for about an hour), and the military could have the ones that turn you into a whiff of ozone and hydrogen.

...the possible deadly outcome is at the top for many folks so, when faced with a victim armed with a gun, more would choose to retreat simply because not retreating can get you dead. At worst stun only gets you knocked out and maybe arrested.

You can wake up from knocked out but not from dead.

However, you can see why their odd perspective (held by some control folks) would fit well with denying the idea of regular frequent DGUs.

A misunderstanding of the nature of most any topic can lead to seriously flawed conclusions.