It's just a part of the glorious contradictions that are human phenotypes. It's not surprising that Mediterranean peoples generate more oil on their skin than others, as the area is riddled with populated islands and produces an oil-rich food culture. Ethnic groups with one or the other (re: proximity to large bodies of water -or- oil-rich food culture) tend to be somewhere in the middle, while those with neither tend to suffer dry skin and hair.

For example, as someone of English/Irish descent, I do generate what I think is a lot of oil on my scalp, but definitely not as much as you, as I can usually go 2-4 days between hair washings without any itch or discomfort. When I do wash my hair, if I remove too much of the oil, it gets unreasonably feathery (think koosh ball poofy), which is its own brand of uncomfortable. As such, I try to use pretty gentle shampoos when the option is available, and when it isn't, I just stagger out hair-washings to every other day or every three days, and stick to washing the rest of the body on between days.

The sad part is, this is easily observable stuff, and people are so busy caught up in trying to create a 'normal' expectation for all people that they discard the fact that our ancestry has evolutionary biology of its own and shouldn't be ignored.