I have scene head gaskets leak due to pitting caused by depletion of the rust prevention of the coolant (electrolysis?) and an article I read said that the while we don't think of it the heating and cooling of the parts causes movement due to expansion and contraction although the term scrubbing was not mentioned that is what is what I am guessing they were speaking of.

Also Cylinder heads and blocks can warp from normal use. If you look inside of cylinder heads and blocks the thickness of the metal is often not very evenly distributed. That means inside of say a block more metal might surround one side of a cylinder then the other side. That means heating and cooling cycles are going to stress the block and distort slightly. The same with the inside of the cylinder head.

On Big Rig Diesel Truck Engines I have seen the occasional head bolts fail. So head bolts can fatigue and lose their elasticity and cause head gasket leaks.

I have also seen one Diesel Head Gasket were the Injector spray (this was a direct injection engine) was not good and focused on part of the head gasket that burned through and leaked coolant.

Getting back to Kent. If you own a Car long enough thermostats sometimes fail to open and fan belts break and you can experience coolant leaks that over heat your engine but don't do obvious damage but in particular stress the cylinder head. So an accumulation of small stuff and time can do in a head gasket.

The pic is from a gasoline engine of mine. The threads of the Head Bolts on the Engine are exposed to the coolant and over Time the Coolant seeped up past the thread sealant and into and next to the head gasket and corroded under the sealing area and got into the combustion chamber.

Notice that the head surface has been cleaned and some surfacing done to it but the pitting is still there. There was also another area of pitting on the other head that was not as deep.

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84 300D, 82 Volvo 244Gl Diesel