HARK, I actually agree with the OPs sentiments....
The whole six thing inserted is sort of a cultural comprimise to make the product more interesting - rather than an objective view of the content. For example, I like game of thrones, but the six scenes are almost predictable because.... its HBO. If there is a chance for nudity, that company will attempt to insert it if its fitting for the demograph without any consideration; that it may actually have more of an indirect affect on keeping the plot less immersive (because of more nudity or more of a portrayal that fake love works) - thus diminishing potential. Sane people like consistentcy in the genre they are entertaing themselves with after all.
Furthermore, nudity is a poloraizing thing inherently among civilized culture: generally speaking, putting sociological boundaries on what's unacceptable forms of nudity. For example, your relatives - most sane people can relate to at least that wall. Again, Im saying this to illustrate that there is a fundamental, inherent thing that people get more grossed out over than say 'killing the bad guy' (which is generally accepted as a good thing).
So yea, illustrating nudity without the confines of some boundary (like sanctity for example) is a bit unreal - or - unbelievable. This, doesn't exactly add to the immersion of the fiction, unless it is attempting to be allegorical.
Tribalism may be a thing that reduces sixual boundaries in reality, but not in advanced civilization - where the baser side (six) is reduced for the sake of higher principles. In Fallout 4, all manner of tribalism is indeed portrayed, but, that doesn't naturally sit well with anyone civilized viewing the content - particularly with cross reality stimuli - ie - im alluding to nudity. It is in essence, more a visual issue, and one that universally illicits a baser side of humanity, regardless of sophistication. Violence is less a matter of the baser side, and more to do with justification in context to humanity. True it may be a natural thing, thus equal to six in regards to it being a physical need, but not absolutely a thing universally correlated to each when it comes to their place and their effects. Simplified: Violence is more an act (physical) as well as six too (physical) but nudity is more a concept/image (mental) as well as justification to kill (mental). The things that reside within the mind ultimately reference to an order within it, that invoke justice, and allude to an ultimate moral law giver.
So with the above rational we should conclude that a nvde picture of a woman in a fake setting is in essence, the same concept to the one that is real and in front of you even.
I'm reminded of Da vinci's teacher making a comment related to this somewhat (unsure of the veracity of this quote, but still an interesting comment):
"His one time master asked him why he always drew people nvde and DaVinci answered, “I want to draw men as God sees them.” His master answered wisely, “But Leonardo, you are not God.”