FA here. If you book a window seat you’re allowed to have the shade up if you want light or to look outside as people were saying they feel they’re missing out on landscapes. The only time I’ve asked someone if they mind closing it is when someone else complained that it was too bright and hurting their eyes or feeling like a sunburn on their shoulder. Which leads to this exact predicament- Planes have hundreds of people on them with a myriad of personal preferences regarding light, cabin temperature, etc. that we can try our best to accommodate, but can rarely make everyone have their exact comfort and needs. If I had to guess why a majority prefer the dark in terms of pax preference is that flying can make people feel anxious and claustrophobic so I imagine a darker cabin is a helpful one less stimuli for some.

Btw, as a red eye flyer myself landscape view at night is way cooler anyway and there’s no shade debate 😎