Because wireless charging is generally achieved through electromagnetic induction.
Electromagnetic induction is a relatively mainstream wireless charging method at present, the principle is to use the magnetic field generated between the coils to generate current for transmission. There are two coils on the wireless charger and the mobile phone respectively. When the coil of the wireless charger is connected to the power supply, the coil plus alternating current will generate a constantly changing magnetic field. When the mobile phone is placed on the charging board, the coil on the back cover of the mobile phone will sense the change of the magnetic field, and the coil on the back cover of the mobile phone will sense the current. Then the current is converted into direct current to charge our mobile phone battery, so that wireless charging is achieved.
Because the thickness of the phone case is generally 1mm, which is acceptable in wireless charging, the phone case is generally plastic, and it will not affect the charging induction, as long as it does not have metal or other conductive materials.