Why can't vampires with sun resistance sunbathe?

because there undead

Interesting thought. I agree that there are different takes on vampires, but there is a consensus, I believe, that they are not alive. That's why they need the life force (blood) of the living to survive. And dead skin can't tan, I would think? Tanning is a process based on the cells being active/alive and working properly, so it makes sense to me. Maybe there is a mod to change that in game.

Aliens can’t tan either. I guess Sixam has a red sun or something :|

Perhaps vampires with sun resistance can't get a tan because their skin isn't damaged by the sun and therefore doesn't need to produce melanin? I really don't know. It kind of frustrates me too as everyone has their own take on vampires and their abilities. I think it would be nice to have the option to sunbathe. I also wish vampires reacted to temperatures and changed their outfits accordingly. In my story, my vampire is basically always room temperature and hates being anywhere cold. He's a bit of an oddball and actually loves sunny weather. Sometimes he seems more like a cat than a vampire. :D

It doesn't bother me, because they are undead being.

For the same reason why vampires with sunlight resistance have reduced or no effect from sunlight reversal cocktails - they're coded that way. I would not be surprised if their skin is coded as unnatural (similar to aliens) and thus can't get a tan. From point of view of lore, vampires are undead. Undead don't work as living do. This is why they're supernatural.

Aww phooey. I guess that private island in Sulani is a no-go. :D

Too bad that the Vamps can't sparkle in the sun.