Cheap materials and a very straight forward construction. The X01 and XX1 cassettes use better materials and a really impressive construction technique. X1 is just an overpriced stamped cassette with cheap steel sprockets. My experience of other SRAM cassettes has been really poor in terms of performance and longevity, so doubt a similarly constructed 11 spd one will be any different.
RRP is relevant as it, erm, allows the comparison of prices (even if Sram's aftermarket prices are vastly inflated). Many people do pay RRP, just not some people here.