The pistol grip really isn't the big advance it's pitched to be, and lets be honest; banning it does nothing in the case of someone who has cracked enough to decide a large number of people are going to die today. It happened to be a feature of a design that won a military contract, therefore the tooling to produce that design was developed, therefore that tooling was put to work to make more due to economies of scale therefore people take the opportunity to post-rationalize tge ubiquity of the pistol grip as being some artificial killing power multiplier rather than just " hey, we can already make these so why not lecerage tge feature to make cheaper guns?" It's more an economic efficiency than anything else.