Why is living in the past so popular a pastime?
I have done this for extended periods - different periods. In my teens it was something like Bath, Somerset (and the surrounding countryside) in 18th century Georgian Times; at another point it has been Concord, New England during the pre-Civil War mid-1800s; at another point it was the Scottish-English borders of late-medieval and Elizabethan times (the time of the Reivers and Border Ballads).
I read and thought so much about this times and places that my sense of them was not just visionary but tactile - as if I could feel it on my skin.
In one sense this is always 'idealised' and may bear little to no relationship to the actual historical life of the majority of the people - but in another sense this does not matter to the process; because this is not a matter of indulging in pleasures or avoiding pains - not a matter of wish-fulfilment in terms of an imagined paradise.
Rather, the appeal is much like living in a Fantasy-world such as that of Middle Earth or Harry Potter - or in some kind of situation abroad when not much is known about that country - the appeal is that the world imagined is wholly-meaningful.
Indeed A world imagined is a meaningful world, exactly because it is an imagined world - intended or not there is both specific-in-detail and general-inter-related meaning which comes from the fact of being imagined.
An imagined world cannot-not be meaningful.
And that is a clue.
Real Life is meaningful when imagined; not meaningful when not.
And for the world to make-sense in detail and overall - it needs to be an imagined world: produced-by and comprehended-by the mind of God.
Before I was a Christian, this imaginative identification felt like an actual need - because 'the imagined past' was the only truly meaningful world in my experience; since I became a Christian, such imaginations (such as Byzantium, late Anglo Saxon England, and the past 150 years of the Intermountain Western USA) are bracketed by the larger and more comprehensive imagination of God's universe.