Maybe the owners have decided to move on to a new place or they need the funds for other purposes.
The Christmas Story House might be for sale because the current owners are downsizing, or there could be potential renovations needed that they don't want to undertake. Another possibility is that they simply received an offer they couldn't refuse.
It could be that maintaining the property has become too costly or the owners no longer have a personal attachment to it. Sometimes life circumstances change and selling a property makes sense.