A closed border with a shared language, shared kinship and a large economic differential produces smuggling, and Punjab's has produced it continuously since 1947.
What moves has changed. In the early decades it was goods: cloth, gold, livestock, and consumer items unavailable on one side. Since the 1990s the trade that matters is heroin, moving from Afghanistan through Pakistan into Punjab.
The methods have included tunnels, throw-overs across the fence, concealment in trade consignments through Attari when trade was open, and since about 2019 drones, which the Border Security Force reports intercepting in increasing numbers each year.
The trade is what connects Punjab's opioid problem to a supply chain that begins in Afghanistan, and enforcement operates against the last few kilometres of a route several thousand kilometres long.
The people arrested are overwhelmingly at the bottom of it. Punjab's prisons hold a large number of people convicted for small quantities and very few for organising the trade.
The trade across the Punjab border now is heroin and small arms, moved by drone since about 2019, which changed the enforcement problem entirely.
Before the fence and before the drones it was gold, cloth, electronics and cattle, and the routes were the same village paths that had been trade routes.
The economics is simple. A border village with no industry, high unemployment and a route across is where a courier is recruited, and the courier is who gets caught.