The answer is that there are many philosophies on how a ball should fit.
Many drillers use what has worked for them. That maybe a relaxed fit, stretched fit, large holes, small holes, lots/little of reverse/forward/side pitches in the thumb, lots/little of reverse/forward/side pitches in the fingers.
Each person has their own physiology requiring a unique fit.
Many shops lack the experience and equipment needed to find correct fits without a lot of experimentation.