Diapauses is a term that designate a slow or stop in embryo development, the reasons for this may be to give hatchlings a fighting chance by allowing them to hatch when flora and fauna id flourishing, more feeding opportunities. This seems to be the only logical reason for diapauses.
However the real question is what causes the egg to diapauses, is it temperature? Is it barometric pressure? A wet or dry period? Maybe its one or a combination of these, however I think its much more simple and strait forward, its right under our nose and we keep looking farther, animals breed when there environment can sustain them, a burst in flora = more quality foods= more proteins, time for cycling and nesting. The more proteins a female intakes the bigger the yolk in her eggs will be, this translates into a longer time for the embryo to absorb the egg’s nutrients, the smaller the yolk the faster an embryo can absorb it, as he is les restricted by space in the egg chamber. This is why an egg can take 300days to hatch while an other from the same specie can hatch in 100 days, to better understand this picture your self in a strapped body harness, even if you have all the food in the world, you can only eat a little, then you must wait till your body processes and evacuate before you can eat again, well the embryo is pretty much in the same situation, the more its constricted by its surroundings the less he can eat = slow growth.
This is my theory from my experiences, it may be totally off or 100% accurate doesn’t matter its interesting nevertheless.
Rgds