High temp is likely but there are many other things that can cause early quitters:
High temp
Low temp
egg or incubator contamination
Eggs stored too long
breeder flock disease
breeder nutritional deficiencies
breeder medication or pesticide exposure
inbreeding
embryological development accidents
improper turning or turning angle
poor ventilation or sealed shells
low humidity
lethal genes
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I realize there can be other causes, but I think it would be unlikely for most things on that list to make every or nearly every egg quit.
I said temp is the likely cause but the majority of those things are also very possible.
Improper handling or failure to fumigate an incubator can cause
contamination that will seep into the pores. Could make every egg quit.
Unless one stores properly or keeps eggs over a week,
eggs stored too long is a likely cause.
Flock diseases can go undiagnosed. Could make every egg quit.
Flock nutrition can be deficient. It takes better nutrition for breeders than that for general egg laying. Could make every egg quit.
It's best to use a good breeder ration. Lots of people like to give their BYC lots treats which can diminish overall nutrition.
Deficiencies in breeder diets of any of the following can cause early quitters - riboflavin, biotin, niacin, pantothenic acid, B6, B12, phosphorus, boron or linoleic acid.
Many people are too quick to medicate. That and pesticide exposure is always possible. Could make every egg quit.
People with small flocks who don't keep breeding lines in separate quarters can easily have inbreeding issues. Could cause many quitters.
Unless one has a reliable turner, turning can be an issue.
Poor ventilation, unless addressed can also be a problem. Forgetting to remove air plugs, etc.. I've had eggs with sealed pores. After the first few days CO2 above 1% is a problem.
Hygrometers are notorious for inaccuracy so humidity can easily be a problem.
While not likely to make all quit, embryologic development accidents can happen in any species at any time.
I'm just saying that there are so many things that can go wrong, telling someone it is always temperature may mislead them and lead to multiple failed hatches until all possibilities are considered.