Don't know why they should care as it doesn't affect them one way or the other. A 30/20 costs the same as a 31/21 so what's the big deal? Even if you do intentionaly break the bat to move up in size the cost of the bat is the same either way, no?
Because of fraud. There are some people that would damage a bat, send it in and ask for a bigger bat to avoid having to buy the appropriate size bat for their DD. Sad but it happens. I worked in the Property & Casualty insurance business for 10 years and saw it happen all the time!!!