No real mystery. Unfortunately, there are many buildings like this in Lisbon. It has much to do with protected rents. During the Salazarist dictatorship, rents were fixed by the state. Following democratisation, the rents remained fixed, and the proprietors have been restricted in the levels of increases they can charge. Obviously, tenants who are on protected rents (usually the elderly) cannot afford to pay the market rate, so they stay put, paying their peppercorn rents. The proprietors in turn refuse to perform any building maintenance. After 30 years without any maintenance at all, a building in a busy and growing city will end up looking like this.
I don't think it's important to know exactly the real story of this building, sometimes it's nicer to invent stories of places, then they become real by themselves, if we put the good dose of fancy in what we create.
I love this photo, it's evocative a perfect starting point for a story.
Marisa
It's been a long time since I took the pictures Adalberto mentioned. But the fire he's referring to, took place in the downtown area called 'Chiado'. It ran roughly from the Rua do Almado till the Rua Carmo. As far as I know, the Rua da Alegria is located near the Avenida da Liberdade, which is north from the Chiado. So I'm afraid that the obvious bad state of the building is due to another disaster or just pure negligence of the owners...
I see stories in this image of course. Beauty for what this once was. Why the disrepair? Ironic that the street is called Happiness. Perhaps memories of a bygone era.