Because it was a 1 day sale price only.
Glad I ordered 8 while I could. Tracking numbers shows the 8 will be delivered tomorrow.
For what it's worth, these are based on the Ultrastar HC530 enterprise drives which is awesome since it is not SMR. These are actually CMR ( PMR ) drives. They do not support TLER ( not truly needed for ZFS anyway so who cares ) and carry a 2 year warranty vs the 5 year retail in addition to no SED and the 5400rpm firmware.
Additionally, these were actually purchased yesterday at $179 each, not $199. This 112TB will give me just a little extra breathing room for Plex