If all manufacturers did the same or had the same thoughts about batmaking, it would be boring as hell. Would save me a tonne of money and space as I'd have less variety to want to buy 😂
I believe they initially introduced it in the Cobra for the Aus range. The thinking behind it was that if you have a low middle, and kept the shoulders and handle thick, you'd need a little more flex in the handle to have a little more give to prevent it from feeling too clunky, and to help prevent breakages.
Reasons why others won't have adopted is probably manufacturing costs, hassle, possibly weight due to more glue and inserts, they don't have the capability to make them consistently, they don't believe there's any benefit, etc etc.