While I would like to believe that DJI values it's customers enough to try and standardize batteries across platforms, I think it's far more likely a confluence of random factors. The TB50 is the largest battery that can be carried on a plane these days and that's a huge factor. For years DJI has been flogged for coming out with an update or new product that always requires a proprietary battery that fits only one product. It costs more over the long run to maintain production runs of many different batteries. They just kind of gave in and went with the flow for now.