The HIV virus is fragile to begin with - blood is a better medium to harbour HIV.
Saliva rarely has HIV to begin - they only theorize that amylase, lysozyme and other enzymes disrupt the few HIV molecules that are there to begin with.
Sweat, tears, and urine are not known to have HIV either for whatever reason.
"HIV in the Environment
Since the HIV concentrations used in laboratory studies are much higher than those actually found in blood or other specimens, drying of HIV-infected human blood or other body fluids reduces the theoretical risk of environmental transmission to that which has been observed--essentially zero. Incorrect interpretation of conclusions drawn from laboratory studies have unnecessarily alarmed some people.
Results from laboratory studies should not be used to assess specific personal risk of infection because (1) the amount of virus studied is not found in human specimens or elsewhere in nature, and (2) no one has been identified as infected with HIV due to contact with an environmental surface. Additionally, HIV is unable to reproduce outside its living host (unlike many bacteria or fungi, which may do so under suitable conditions), except under laboratory conditions, therefore, it does not spread or maintain infectiousness outside its host."
http://www.cdc.gov/hiv/resources/factsheets/transmission.htm
Laboratory environment - this includes temperature and a suitable medium.