I think there are several things at work.
- First, there is a psychological tendency to assume that smaller guns - not just smaller grips, but smaller guns - will be easier to handle.
- I think some of this is because of people's real world experience with tools and machinery where it is often true. It is easier to handle a compact car than a delivery van/box truck. It is easier for most people to be precise with a 4" paring knife than with an 8" chef's knife. And in sporting equipment, it's usually true that women's models of sporting "tools" will usually be lighter and slightly smaller, particularly when it comes to things held in the hand and swung (like bats or clubs or racquets).
- This assumption gets reinforced by movies and TV shows involving guns, where the women characters often shoot smaller guns, and where bigger guns typically have more recoil/flash. Dirty Harry had a big gun, and it had big recoil. Black Widow shoots a pair of Glock 26 baby glock sub-compacts, and those guns don't do anything in her hands but have the slide reciprocate (because they are prop guns not launching anything but a puff of flammable gas). This trope is so well ingrained that the original Men In Black movie made a joke of Agent J being given a small space gun (the "noisy cricket") that actually had tremendous recoil. A small gun with a lot of recoil is a joke in Hollywood - whereas in real life, I have personally characterized the recoil of .357's from a J-frame as "no joke."
- Second, there is a further psychological issue that many people, especially women, are conditioned against gripping things hard, and are further conditioned to only need to grip small diameter things with force. When do most people (especially women) use a significant percentage of their grip strength? Typically when lifting/holding things with handles (shopping bags, suitcases) or when using some handle to partially support their body weight (grab handles on car door frames, stair railings). These are most often small-diameter holds, with the hand almost a clenched fist. For people (including most women) who don't squeeze plier handles very often, squeezing hard with all the fingers on the left hand back against heel/palm, and doing so at a time where the hand is half open is rare. The muscles aren't well developed, and the psychology of clenching hard before the hand can even get nearly-closed is foreign. Given that one of the most common problems for newer pistol shooters - even those who are well instructed - is applying sufficient force (especially with the weak/non-dominant hand), this is a big deal. If a smaller diameter grip is going to pyschologically induce more willingness to clamp down harder with the left hand, that's going to (not unreasonably) feel like something that the user can get more control over.
- Third, there is the very real issue of trigger reach. The conventional wisdom is that it is best to actuate the trigger of a pistol through the motion of the proximal joint.
The CW is that it is ideal for
only that joint to move, with no pivoting of the distal joint required. That is generally going to be easier if you can get the proximal joint far enough forward to be roughly in-line (when viewed from above or the side) with the trigger's pivot/travel or only somewhat behind that point. And for heavier triggers and/or with longer travels, it can become very difficult to apply enough force
in a controlled manner if that proximal joint is very far behind the trigger... you necessarily have to use a clenching motion, rather than a single-joint pivot/press motion.
Now, working against that, you have certain physics realities. One is that a larger, heavier gun will have less recoil velocity than a smaller, lighter one. And a longer barrel will generally have less of the blast/flash that is so bothersome to newer shooters and so inducing of blink-involved flinches. Another is that, if one is actually
using their weak/non-dominant hand appropriately, getting enough grip surface exposed on the left side* of the gun
after the right hand is in place requires a certain amount of size... often a little more than newer shooters think is ideal.
So, in conclusion, I think someone choosing a gun for a newer shooter needs accept certain trigger reach needs, and then generally go as large as can be tolerated for the purpose and not be physically exhausting to hold in a firing position for a minute.
*Assuming a right-handed shooter.
