Sometimes you wind up with people who are just very selfish and don’t care about anyone other than themselves. It is a shame that the landlord doesn’t care either about anything other than collecting his rents. He should have told the tenants that there are rules of common courtesy and there are legal rules that the community have to abide by. He should then have set the rules for ALL his tenants according to city guidelines which are no noise past 10:00 pm and not before 8:00 am or 9:00am depending on the city ordinances. Of course he could adjust it according to what is fair and appropriate to the needs of his tenants. IF he doesn’t wake up, he will either have to get rid of the upstairs tenant of deal with an empty downstairs apartment.
There are always going to be spoiled and selfish people who thing “haolam nivrah RAK bishvili”. The world was created just for me and not give a hoot about anyone else. That is a true shame, but Hashem usually opens their eyes sooner or later with a nisayon of their own which they don’t usually understand at first.