Quite likely, the way C18th readers lived at night with candlelights, shadows and less protection from the elements like high winds & storms, gusts of wind suddenly blowing out lights--- so it may have been easier for C18th readers not only imagine but identify with the setting of Otranto.

Makes one appreciate the electric light-even if it isn't JA. ;)

People were superstitious, (I think the last witchcraft trial in England was early C18th or late C17th. Yet about the time JA ws born a woman was burnt to death-though hung first.)

People turned out to watch public executions, yet feared the supernatural and later horrid books became a craze.

My impression is they may've had a fear and a fascination of such horrors.

(Like modern people have with horror movies !)