The reason that cranks break at the pedal-eye is, more often than not, according to TA, because the shoulder of the pedal axle has been allowed to cut into the surface of the crank thereby creating an "incipient crack". It is to prevent this happening that TA always supplied thin brass washers to place between the crank and the pedal. In recent years some manufacturers have beefed up this part of the crank's surface by adding into the forging or casting a few extra "thous" of an inch of metal. That might be an improvment but it does not prevent the axle from actually chafing into the alloy of the crank.
Another reason that might cause the pedal eye to break is fitting a "tight" pedal thread into a slightly "tighter" crank thread as sometimes this can lead to tearing of the thread inside the crank. It is always better in such circumstances to carefully tap out the threads, and always use some form of lubricant when fitting the pedals.
Norris Lockley...just wiping my hands on an oily rag