Most of the sharing of HIV is done by people who have NO idea they have it. In the ID clinic I worked in for 2ish years people either get tested because their partner just tested positive OR they eventually begin to have AIDS symptoms.

Thrush - people have soar throats and can't swallow anymore.
Rashes - people go to dermatology to figure out a rash (3 of them in dermatology for a YEAR before a blood test was ran - all 3 had AIDS all three were straight men.)

Because the incubation period is so long, you could be spreading disease and not even though you’re positive for years

because first off, someone had the virus and never got tested for it. So they didn't know they had it. Then they gave it to somebody else. Well that somebody else didn't know they got it from the previous person, and they give it to the 3rd person not knowing that they had it. Now you get 10 people down the line, and by this time the very first person is just starting to show symptoms, and they had been with 20 people by this time. It's just a vicious cycle. The only way to truly stop the spread it to have literally everyone on Earth take prep, and the spread would eventually die, if everyone who had the virus stayed on their meds. Which we know that isn't possible because the drug users would forget their medication for days as they are strung out and share needles and have sex. So, in the end, it will truly never end until there is a cure.