1.- I don't have a Housecarl for Riften. Or a wife that could stay there, reason i'm saying this is because I heard that if you don't have anyone in your house, there could be robbers who come in and take my stuff. And the whole point of me having a house in Riften is because my house in Whiterun is cluttered, full and I can't find stuff anymore, since all chests and storing objects have 100+ items already.
2.- IT'S RIFTEN. Home of the thieves, and nothing asks more ''STEAL FROM ME'' than storing all your valuables in such a place. This also goes back to my housecarl thing I was talking about, if there's no one inside, people could go in and steal (regardless of it being Riften or not)