wannabe-aviator, there are some cargoes which are worth paying a lot of money to move around quickly, even if they are small payloads. Car parts are a great example. Many small operators around the world pick up small loads of parts as many manufacturers operate on small amounts of 'just-in-time' inventory. The cost of air freighting them in so that they can be 'just in time' is offset by not having to have large amounts of storage, and the accounting charges that would incur.
There are many other types of cargo that are light, sometimes a little bulky but are time-critical and many operators around the world make a niche out of carrying them. While it may seem insane to send some things by air (read the 'Strangest Freight' thread), for some it makes sense and they are willing to pay for the privilege.