Full sized Glocks are imported with with the smooth faced trigger. Compact and sub-compact are imported with the grooved trigger. Why?
To meet BATF import points. The grooved trigger is considered a "target" trigger and as such adds the points necessary for import. It's stupid and draconian, but it is the law.
I suppose a smooth trigger assembly could be retrofitted.
To qualify for import, a pistol must score a total of 75 points.
CHARACTERISTICS
POINTS
Length:_ for each 1/4" over 6"
1
Forged steel frame
15
Forged HTS alloy frame
20
Unloaded weight with magazine (per oz)
1
.22 short and .25 auto
0
.22 LR and 7.65mm to .380 auto
3
9mm parabellum and over
10
Locked breech mechanism
5
Loaded chamber indicator
5
Grip Saftey
3
Magazine saftey
5
Firing pin block or lock
10
External hammer
2
Double action_
10
Drift adjustable target sight
10
Target grips
5
Target trigger
2