system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come you don't get HIV or AIDS from mosquito/bug bites?
gpt
Diseases like yellow fever and malaria are spread by mosquitos through their saliva, not because you got a little bit of the infected person's fluids. Yellow Fever and malaria are just two examples; but virus's/infections that are spread by mosquitos have evolved a way to avoid being digested with the blood that carried them. Instead of being digested, they make their way into the mosquitos saliva system and infect more people.

Aids and HIV don't have this survival mechanism. When a mosquito sucks the blood out of a person with aids or hiv, the whole virus gets digested before it can become spreadable.

There are 2 more factors that also limit this. One is that a person with HIV or aids doesn't have enough of the virus floating around for the mosquito to take enough to infect with.

The other factor is this. Most people think of mosquitos as essentially flying needles. The mosquito's "needle" actually has 2 canals, one that handles drawing blood in, and one that handles saliva. Even though mosquitos do vomit on you a little bit when biting (how you get yellow fever and malaria, from infected saliva), the saliva canal isn't connected to its stomach, so theres no way for aids infected blood to get there.

short version:
aids and HIV are digested too fast to be spread
there isn't enough aids or hiv to be spread
theres no way for aids/hiv infected blood to get back out of the mosquito once its in there.