First off if it is heating quickly it will be throwing off the dissolved air in water quickly. Comparison with water that has boiled then allowed to cool (thus removing a lot of the dissolved air) might be illuminating.
And the fact it is a rapid heater is not a cause to believe it is a rapid cooler. These things are made by slave labourers in Chinese prisons or on a free market where the workers are paid something like
5 pence an hour and work 80 hour weeks.They are not going to be highly motivated with those Victorian conditions, are they?
30 years ago a kettle had chrome plate and was fitted with easily repairable elements. Build quality was very very good. (For the era.)When I fill my kettle I put one pint in it and pour one pint out (as I drink tea or coffee in 1 pint mugs.) Immediately I empty the kettle, I refill it as I don't like the idea of the thing overheating. As an earlier poster stated, it is embedded and cannot cool like the old fashioned type do.
I presume that is the answer to why they don't seem to last long, though I may have just been unlucky initially. I cannot say.
My first experiences with the style was the poor longevity experienced by other posters on this thread but with this immediacy about replacing the water, there has been no problem.