I can answer that question-it’s because the trigger pull is so light. Too light for a pocket gun, in my opinion.
That’s why I ordered mine with the thumb safety. The safety was too hard to flip on and off for practical use when I first got it. But after switching it on and off repeatedly about 2,000 times while watching TV over several nights, it has finally loosened up enough to use while carrying.
If anybody ever comes up with a higher profiled replacement safety lever I will be at the head of the line to get one.