Why aids is not considered as communicable disease?

It is not a communicable disease because AIDS is a clinical diagnosis regarding late stages of an HIV infection, where CD4 counts fall below 200 and/or the individual has at least one AIDS-defining illnesses, which are illnesses found only with that degree of immune suppression along with a positive HIV test.

If an individual has AIDS and shared needles with a friend who was not HIV positive, they would not be giving their friend with full-blown AIDS. They would be infecting their friend with HIV.