Because there are not that many algorithms coins that can be mined only on cvp13 and can sustain a thousand of these devices.
board based on dual arria 10  (comparable with bcu1525 by logic resources and  performance at a half price) is coming to market very soon. so bcu1525 owners are already loose 2x in terms of hash cost

this is a tricky example because only a few hundreds fpga bords mining these algorithms atm. almost all BCU1525 units are on lyra2z bitstream with 3 bucks/day income