Of the estate pipes I've bought, the cracked ones were almost always ones with tons of cake in them. I think when a cake is kept uneven it disperses heat, expands and shrinks at different rates which can stress the wood more and lead to cracking. Possibly the thicker walls enhanced with cake buildup could cause someone to smoke the pipe hotter as well.
A couple of my large Danish (mostly)straight grain pipes have cracks in them. They had lots of cake and are in the chunky thick Danish freehand style. Definitely smoked heavily, so I can't say the cause. The cracks are still growing, but I got them for super cheap thrown in with some other pipes I bought off someone and they smoke great, so I don't mind. Alot of times a crack will take years to develop and won't really even affect smokability for a long time.
It all depends and is somewhat unpredictable, sometimes a thin small pipe can take alot of abuse and sometimes a thick pipe will give up at some point. But stress is the key factor. Keep the cake even and heat distribution even and it should last longer. A pipe will eventually wear out, but it might not be for many many years, and the less stress the wood has, the longer it will last.