Re: Belt Drive vs. Chain
To take a guess I would say that because most of the kits are built to the same standard (not so great). I am guessing that it costs more to have a workable rim (for the belt to pull) then it costs to give you a crappy sprocket. Though in some ways the chain is a little easier to use. It doesn't stretch out and it doesn't need replacing as often as the belt. It DOES need some basic maintenance on that is basically the same as a normal bicycle chain. These kits are made for the average joe to throw on his bike and the people who designed it probable assumed the costumer would already know basic chain maintenance.
Again, this is just a guess and I don't own any belt drive bikes. I have heard they are great but that the belt needs occasional adjusting.