Not a lot of room in the turret of a WW2 era tank, with commander, gunner, loader, dirty-great gun breach and ready-use ammo. Like many aircraft of the era, a "wireless set" took a lot of room, was complex and needed a crew member to handle it as a primary duty so, put it in the hull. Wireless operator would generally have secondary duties of hull machine-gunner and driver's assistant.
Interestingly, many German tanks also had a facility to rotate the antenna down into a protective sconce when not in use. Perhaps your model has this?