Higher end track cranks are made much stiffer than the average crank, which takes much more time(and money) in design and construction. They are also designed with tighter tolerances which takes more time and money. High end cranks have as round of bolt circles as can possibly get, compared to lower end once, which also take a lot more time and money.
Lots of smallish things combine to make prices of really nice things higher than low end ones. Just like everything else.