It's because the WiFi frequency bands are publicly owned. They don't have the legal authority to ask for consent to deauth because they don't own the channels in the first place. Intentional interference can get in the way of municipal internet access, it can cause safety problems (some channels in some bands are reserved for safety equipment), and of course it can be anti-competitive. Private entities are only being allowed to use WiFi bands in the first place under condition that they will not intentionally interfere with other devices.