>>212806549I think it's actually a part of the generation/age thing that I outlined, but in an additional way.
There's definitely "trends" in what faces and bodies look conventionally hot or attractive, and they come and go decently fast, and get replaced by new faces that fit the newer trends instead. So if you were born (for example) in the early 90s, then you'd have hots for some 00s babes, and you'd also be "raised on" late 90s babes to some extent (maybe with less impact because you probably didn't hit puberty then). But the sex symbols of the 80s or early 90s would mostly be of different face types, different types of sex appeal, etc. So, on average, you wouldn't be very likely to be attracted to someone from earlier eras than your "expected" era of sex symbols.
But go back far enough, and then it's distant enough that it's not "eww, it's girls who my older brother finds hot", it's just abstract attractive women. There's also a certain vague cyclic nature of trends, so maybe sex symbols from the 70s or 40s have enough in common with those from the 00s that you can find them hot again, despite them being "too old" for your expected attraction bracket.