Why didn't the european people develop slanted eyes if they live the same lattitude as east asian people?

interesting question Europeans did spend a longer period of time in ice age conditions. Also it is possible Asians descended from an African population that already possessed epicanthal fold. Africans populated Eurasia in different waves of migrations, One or several of these may have been of humans who possessed epicanthic folds.The oldest people genetically are the Khoisan peoples of South Africa, The Khoisan and other African tribes posses epicanthic folds also, It is also possible the Asian ice age climate had more whipping winds. The Asian/Mongoloid haplo group O is thought to have developed in the extreme north Eurasian regions. Having developed in this area may be a factor also.. It is known that the sunlight is refracted differently in northern latitudes and that vision is more difficult the further north you go. It is still some what a mystery why epicanthic folds evolved in any peoples

The epicanthic fold, also known as Asian eyes, is believed to have evolved in Central Asia as a way to protect the eyes from the cold, sunny and windy conditions of that area. Europeans are not all from Southern Russia and Central Asia. The Cro-Magnon, from whom Europeans are descended, lived in Europe for tens of thousands of years.

probably the "pure luck and chance" portion of evolution

Same latitude =/= Same climate For example, Toronto is further south than London, yet they are different climates.

Genetic benefits, such as the slanted eyes, shows up a random. A random genetic mutation that benefits one population might not occur in another population, even if the living conditions are the same.

Europeans were always much too confident and individualistic to develop slanted eyes. Confidence enables bright piercing eyes that will peer into your soul and colonize your countries.

I am no genius on the matter but Europe ain't a cold place. During the small Ice age 10.000 years ago it was but not since then. Just a bit cold in Northern Europe during winter but that's about it.