even with the large volume printers the cost of toner is greater than the cost of professional large volume print. We have a large volume printer and it is cheaper to get long runs printed. The quality of print is also a factor and buying paper in small volume is expensive. Above any thing else the quality of presentation is paramount. I have seen lots of homemade leaflets printed by individuals that although, they think they are fine, they do look very amateurish.
When an individual leaflets works out at about a penny why would any body want to go to the trouble of delivering something that is not 100% or reduce the response rate in any way.
Like many things printers invest a lot of money in their equipment, it is a bit like comparing a rug doctor to what we do.
We do print short runs to cater for specialised markets but it is just not worth the effort on volume.
Peter