It seems to only improve in a single area (genetically) so much before switching, it doesn't optimize, it is focused, and the rate of evolution is driven by stress.

My theory is that too much success would cause a population boom and bust, and so it's encoded into terrestrial life very early on - the studies come from bacteria genetically edited to break respiration pathways, and all the evolution was focused there before the evolution moved to a different area - but they didn't even recover their original efficiency, possibly because they just reached a comfortable point without competition

So in this case, I think the female hyenas were probably being killed opportunistically, which led to evolutions related to size and dominance. Bigger females that fuck the males in dominance rituals are enough to relieve the evolutionary stress, and so evolution slowed and they reached "good enough"