Pistols require less ability points to be effective in them.
Can you give a more in-depth explanation? I am not sure I am following you here.
For example, you can get just PER6, set STR/DEX/AGI at the minimum and still be able to have pistols as decent "backup" weapon.
On the other hand, SMG need AGI6 for Spec Ops, at least average PER, and high DEX is crucial to be able to burst more then once per turn. And Full Auto feat for better bursts requires STR 7.
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If on the other hand, you want to specialize with Pistols, you need DEX, but then with high DEX it makes more sense to specialize in SMG, since gains are higher.
In fact, for STR3 SMG character, pistol can be nice backup option with powerful Aimed Shot attacks, when they make sense over burst.