The reasons for this are as follows:
The FET also has a certain voltage at both ends when it is charging, and it is impossible to be completely ideal when there is a voltage drop on it, there will be power consumption, so it will be hot
There is a transformer inside, the copper wire has current through, the heat is normal, the charger heat slow in summer, easy to hot, the charger electrical components aging also heat
The output current is too large, so add a current limiting resistor