Hear me out

Watch Call of the Night (anime), going outside at nighttime is actually introvert paradise (and vampires too)

However, how would you explain the “social behaviour”, like only entering if asked (other than the fantasy of an author)?

i'm not sure whether this is a real question or a joke but here's my take:

The vampires for one are a metaphor in the first place, and secondly they have been heavily "demonized" - i.e. made to look bad, partially because an enemy wanted to discredit them.

The stereotype of a vampire in the medieval ages was a person who (a) was highly intelligent and (b) often was a landlord or some other noble person having a castle and such.

Due to their duties (mostly organisatorial stuff) they had to be highly intelligent, otherwise they couldn't have managed to organize a society. So they had to study a lot, including reading and writing lots of literature, which was done indoors, so they became of pale skin and faint musculature. Subsequently, their body adapted and it became more difficult spending time outside, partially because the pale skin was more susceptible to the sunlight, partially because their eyes were adapted to rather dim light instead of the bright light of the sun, partially they weren't accustomed to the noise that is typically heard in the daylight (such as in villages where children scream and people work), so they preferred the quiet of the night, and so there was a stereotype that they would always be awake in the middle of the night, but not so much in the daytime, especially not in the early morning, when most people got to work.

I guess a lot of the rest is mostly due to authors trying to sell more copies and trying to overblow their point and make the story more exciting for the reader.