Ipad
Why can’t you charge an ipad on the wireless charger? You still have to plug a cable into the wireless charger pad.
iPad, iPadOS 14
No model of iPad support wireless charging. There is no inductive coupling coil inside the iPad as the aluminium chassis/shell blocks inductive charging.
BY contrast, iPhone models that do support inductive charging have glass back-shells - plus the necessary inductive coupling coils and associated electronics.
Direct charging is also considerably more efficient than inductive charging. As iPad batteries are considerably larger than iPhone, inductive charging would be comparatively slow.