Why are mobile device charging cables so short?

mobileMobile devices are not meant to be used for voice calls while the device is charging.

TRUE: The horror pics circulating the Internet of phones exploding is a hoax.

This does not mean these devices are safe to hold to your head while they are being charged. All the tests and working procedures are done when the phone has sufficient charge and is not plugged into the power outlet. Using the device in this manner is therefor not what the manufacturer had in mind.