I'm wondering why are gay people more likely to contract aids or hiv?

They are not. Aids was first identified in a population of gay men who engaged in anonymous sexual intercourse with multiple partners without protection. This behavior puts one at risk for HIV infection, just as sharing needles for IV drug use does. Gay men who do not engage in unprotected sex are at no more risk than straight men who do not, and multiply promiscuous straight men are also at risk.