A) The west just has fewer people. The most populous country in Europe - Germany - would be only the 10th most populous country in Asia.
B) A substantial amount of people in Asia live in rural areas. In India, nearly 920M people live in rural areas. The lack of infrastructure in rural areas means that things can happen that never ever reach the local authorities. People can simply slip away without a trace.
C) State power is weak outside of major population centers. Corruption is rife. Povery is rampant. Earning opportunities are limited. Combined, it means that criminals know they can get away with anything as long as they bribe the right people.
D) A substantial percentage of Asian population lives under failed states (same for Africa). State power isn't just weak; it's absent.
E) Asia is just way too large and geographically diverse. Easy to hide away illicit activity in a dense rainforest or deserted mountain than in wide open plains and farmland.
"State power is weak" is a weird claim since the powerful states don't prevent trade with slavers.
Powerful states like US and China run slavery operations directly. It's even explicitly enshrined in the US Constitution.
The US didn't become a powerful state until the Constitution was amended to ban slavery.
The Confederacy, for example, was militarily and economically a very weak state. It couldn't even supply shoes to its soldiers. It was unable to pierce the blockade on them by the Union. And so on.
B) A substantial amount of people in Asia live in rural areas. In India, nearly 920M people live in rural areas. The lack of infrastructure in rural areas means that things can happen that never ever reach the local authorities. People can simply slip away without a trace.
C) State power is weak outside of major population centers. Corruption is rife. Povery is rampant. Earning opportunities are limited. Combined, it means that criminals know they can get away with anything as long as they bribe the right people.
D) A substantial percentage of Asian population lives under failed states (same for Africa). State power isn't just weak; it's absent.
E) Asia is just way too large and geographically diverse. Easy to hide away illicit activity in a dense rainforest or deserted mountain than in wide open plains and farmland.