New thermocoupler resistance problems

The only problem I have with my printer that happens so often is this

all I wanted is understand when and why I have to change my heater&thermocoupler since you suggest to replace them after 400hrs but I have 7700hrs in it and I still see plenty of life in it since resistance is lower than the new units I bought

I’m referring to an old topic that refers to an old printer, why the informations were right once and no more today ?

Thank
Roby