The thought never occurred to Chris and Barb "Hmm, if we hoard again, will there be another fire?"
Of course there won't be another fire. The fire wasn't their fault; they did nothing wrong. It was all on the Keurig company's head for selling them a fire starting coffee maker. /sarcasm
Chris and Barb never, ever recognize (or admit) their own mistakes. This is one of the reasons why they never learn, but keep making the same mistakes.
They even acted like belligerent slobs in the rental property.
I believe it took more than a year to make that place rentable again once Chris and Barb left.
That actually is in keeping with my view that given the choice between spending some money on something sensible or using something stupid that they already have, they'll choose the latter.
They'll do whatever takes the least effort, and not care about the expense (it's not like they earned that money, after all). If it's easier to use an existing cord they'll use that, but if it's easier to buy a new cord than to find (or dig out) an existing cord, well they won't think twice about wasting the money.
Really, though, it doesn't matter what particular cord they used, because what they did with it would cause any cord to fail eventually.
I can't see a "heavy duty" extension cord fraying that easily.
I can. "Heavy duty"refers to the thickness of the conductors, not the strength of the insulation coating. The thicker the conductors, the thicker the cord, and the thicker the cord, the faster it would be wrecked by being crushed in a door jamb. This is a case where a thinner, lighter duty cord would actually have lasted longer before inevitably failing.
The only frayed extension cords I've ever seen (and gotten rid of) were ancient and skinny.
But were they repeatedly smashed between a door and the doorjamb?
To get thin enough to heat up to firestarting temperatures in a couple minutes of a Keurig cycle has to be seriously frayed to the point the cord is barely holding together.
That's not how the fire started. The Keurig was off when the fire began, and likely had nothing to do with it.
What happened is the repeated crushing of the cord in the doorjamb trashed the cord's insulation until it failed and allowed a short between the conductors. The resulting arc was more than hot enough to ignite the door and frame, and didn't need the Keurig to be in use, or even plugged in (though it was). If you keep crushing an extension cord it will eventually spark up even if nothing is plugged into it.
This is why most modern electrical codes require arc fault protection on circuits with outlets, but 14BLC was too old for those codes to apply.
tl;dr: The fire was started by an arc in the cord, not resistive heating under load. Keurig did nothing wrong.