Someone recently infected with HIV can potentially pass it on to others whilst not being detectably infected. It makes sense to limit those who engage in high risk activities until sufficient time has passed that they will now test positive. The full criteria is here:
"You should not give blood if you have AIDS or have ever had a positive HIV test, or if you have done something that puts you at risk for becoming infected with HIV.
You are at risk for getting infected if you:
have used needles to take any drugs, steroids, or anything not prescribed by your doctor in the last 3 months
are a male who has had sexual contact with another male, in the last 3 months
have taken money, drugs or other payment for sex in the last 3 months
have had sexual contact in the past 3 months with anyone described above"
https://www.redcrossblood.org/donate-blood/how-to-donate/eli...