if you can find a cable with smaller strand/higher count wires.. use it.
the thinner wires bend easier, reducing the flex forces.

other than that... change cables more often.. it's what is done by any of us that have ever fought to remove the broken remnants of drop bar brifter shift cables.

VERY common on some Shimano brifters, btw... TOO common.

it would be a good thing to look into... WHICH cables flex easier... it would be a popular article for sure.
higher nickel alloy stainless steels Should resist cracking better, too. Nickel lends ductility... Chrome and manganese are the opposite of nickel, in that respect...

plain old galvanized cables may hold up longer in the tight bends required in brifters.... ?....

Jagwire or Clark's need to get to work on brifter-specific cables, IMO. I'd buy a few pair!
although.. flexing is stretching, so...