Because next year at this time the market will be flooded with used ARs(preban). That will drive the price/value down. Even if it is NIB, its still just a SP1.
Why would you want an SP1 receiver after the ban sun sets, when you could get a BM, DPMS etc... for the same price? I do not think the price will drop down to the $500 level for a complete rifle, though.
....But, since it is an SP1, it might also hold value or become a collectors item. Who knows?
Lets just hope the ban dies and doesn't come back with even more bs signed in it.