Why are soldering tips worn out

Tip life TOP
Point 1 Solder corrodes the iron-plated part and makes a hole.
Point 2 The solder-plated part is oxidized in black and the tip is no longer wet with solder.
Point 3 The surface of the heating element insertion part oxidizes and the heat conduction becomes poor.
(*Except for tips in composite type which has different structure)

Point 3. The surface of the heating element insertion part oxidizes and the heat conduction becomes poor. (*Except for tips in composite type which has different structure)

*If the tip, tip enclosure(pipe) and heating element are oxidized completely, they should be replaced with new ones.