What made dark skin unfavorable

Since we all came out of africa thousands of years ago, our ancestors probably had black/dark skin, so when we eventually spread to places like europe, why did we develop white skin?

Mainly the climate and day length (in that the further north you go the shorter the days in winter are) and the intensity of the sun (in that the further from the equator you get the less intense the sun is).

People with dark skin would not have got enough vitamin D and become deficient more than lighter skinned people. Because vitamin D deficient people were less healthy as a result they produced less offspring than the more successful fairer skinned people.

Eye colour is associated but apparently evolved differently, in that blue eyed people see better at night as more sunlight goes thru the iris and into the eye (in the same way that dark pigmentation in the eye prevents too much sun getting into the eye and helps prevent eye damage eg cataracts, blindness to sun damage). since the sunlight is less intense and the nights are longer in the winter, it was more advantageous to those who had the lightest coloured eyes, so they would have become more common over time.

i thought it had something to do with the sun. and how much sun exposure people got.
people are always darker closer to the equator.

maybe whiter people stayed indoors a lot too, because of cold and stuff.

Due to the different pigmentation between the people who migrated. And adaption to the weather conditions in those parts of the world.