Every tumor is a group of cells whose growth went uncontrolled. These cells need a blood supply same as any other cell in the body in order to survive. As a matter of fact, the tumor cells need a blood supply even more, because they present an area of rapid growth which needs a rich blood supply providing enough construction material for the new cells.
The tumors produce certain molecules that act as triggers for producing new blood vessels in the tumor. There are even certain medicines that act on stopping the effect of these molecules, thus reducing the process of creating new blood vessels and significantly increasing the chances to slow the tumor growth.
The problem with the fibroid tumors is that they are more or less in the uterine wall, and the newly formed blood vessels cannot be distinguished, during operation, from the normal blood vessels which are responsible for the blood supply for the rest of the normal uterine wall cells.
You might want to consult with your gynecologist or ask for a second opinion from another gynecologist about your condition and the possible treatments.