Comment by longtom

Because Western imperialism is very likely only a secondary cause, if any. You see strong condemnation of sodomy all across Sub-Saharan Africa, Middle East and South Asia, with an extremely wide variety of religious and practical (STD prevention) underlying motivations, even in regions without any history of imperialist occupation, and such cultural norms are stronger in regions with higher birth rates, higher infectious disease death rates and lower hygiene standards.