Two key reasons.
- The underlying chips that make both the transmission and reception of wireless power are very expensive. The PCB (circuit boards) and metals used are very common, but the actual chips that do all the work are not cheap. There are few companies that offer them right now.
- Wireless charging is relatively inefficient, which is why it releases a lot of heat. To minimize heat you have to do a lot of tricks including passive air cooling, as well as decently complex magnetic field compression via uniquely located magnets with the opposite polarity of the main field.
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