Why are aerosol-type butane canisters so much cheaper than screw-thread iso-butane canisters?

Standard 227g pure butane canisters contain about the same amount of gas and heating power as a standard 230g / 8oz screw thread canister, but for one third or quarter the price.  At several degrees above freezing point, the two types of canister are more or less interchangeable. The butane canisters are very cheap because they are made in huge volumes for domestic cooking, BBQ and picnic stoves throughout East Asia and worldwide. A typical aerosol can production line produces 120 cans per minute and there are many production lines worldwide. They are also widely available in the west through Asian food shops, hardware stores, camping stores and other outlets. In east Asian supermarkets, a 4-pack typically costs $4.50 or less in the USA and around £5.50 in the UK (from Koreafoods.co.uk). Such general retailers sell large volumes of aerosol-type butane canisters for a small margin.

Screw thread canisters iso-butane/propane canisters for camping and backpacking are made in much smaller numbers, use thicker metal and more expensive valves (as they are more highly pressurised). Virtually all stove companies and other outdoor gear companies spend a lot on promoting their own brand of canisters as well. And they are generally only available from a narrow range of retailers i.e. outdoor gear shops and some hardware stores. 

The result is that although the heating power of the two different types of canister is about the same above freezing, screw thread iso-butane / propane canisters are much more expensive.