I think the rented apartment is the only loose end that needed tying up.Agree most suicide victims don't leave a note, sadly.
But people are saying, most don't contact their landlords either. But maybe -- what you say to a landlord is "business" and not emotionally fraught, unlike what you'd feel writing to family. JMO.
Perhaps they felt distant from their other siblings and family, and didn't wish to leave a note......or perhaps that may have been quite close, and couldn't bring themselves to write a note to them.
It's easier to send a message to a landlady about the rental agreement and that you won't be coming back. It's easy, matter-of-fact and there is no emotion attached.