At a most basic level its supply and demand. Looking deeper I would say its a combination of TP people thinking they are getting a great deal and naivety as a whole.
I wonder how many of the pay to fly brigade will jump from somewhere like Ryanair thinking I don't mind going to work for sh*t money cos its a big jet and a stepping stone onto something bigger and better. Their plan will be to stay for 2-3 years and then get into Big Airways now that they have heavy jet experience.
Problem is that in taking what is a pitiful amount of money to fly a 744 it brings down the T&C's at Big Airways and the grass is no longer greener.