Old buildings require at least one major renovation every year such as a new roof, replacing the plumbing underground, and seismic retrofitting. If the owner hires a licensed contractor than the cost may exceed the property's net profit. However, if the owner is a licensed contractor and can do most of the projects alone than he or she could make a profit.
It costs approximately $10,000 to dig up and repair underground plumbing, which is absolutely necessary for old apartments that were built before kitchen sinks had garbage disposals and women used tampons and wore artificial hair extensions.
Another major problem is parking. During the 1950's most households had one car and so the apartments that were built during that era had one parking space per unit and the houses had a one car garage.
To a lay person it would seem as though repainting the exterior would be an easy DIY project. However, if it was built before 1978 than the old paint contains lead and so the job requires a licensed paint contractor who has special equipment. It costs over $30,000 to have an 18 unit building repainted by a professional.