Why do Android users do not have this option to disable charging of the phone by the controller in the menu??

Apparently its there for ios users.

C'mon DJI ...

been requested 1000s of times and falls n deaf ears.  

Hello and good day. Thank you for raising this concern today. The reason for this concern is it is related to the android system and hardware. The Android phone needs on-going 500mA to maintain the USB connection, so there is no option for the Android device to disable the Charging mode. Thank you for understanding.

Thanks Stephen

Has someone made a comparison by what percentage this reduces the Remote Controller Battery life as opposed to having charge disabled on an iOS device,?

The Android is a way different from IOS. When You say Android, you have to keep in mind that are so many Android variations, that it is often impossible to achieve desired result on all of them