I think it's because the prices are already as low as they can be....
The market is so small at the moment that there are very few levels before motors/batteries/etc..... go from factory to user.
With large production items you get Factory,Sales,Distributors,Vendors,Stores,Re-sellers,Mom and pop shops.. etc... by the time a product is sold to the consumer it has inflated many % .
Example, i purchased from Crystalyte, i build and sell the bikes, I base my prices on what the other dealers are asking as a general rule and there is very little profit to be made .. It has to be fun to make it worth the effort !
If the E-bike battery market is the same as this model, any less and the vendors will not be around for long before going bankrupt.
There is more to a battery pack than it's price !