While we can be quick to claim hot topics as 'DRM' or 'Poor Economy' for the cause, it's more likely the simple fact that the difference between BluRay and DVD is negligible.
DVD from VHS brought 5.1 surround sound and full digital picture. There was also the elimination of over-use causing damage to your tapes and of course the dreaded RE-WIND.
BluRay brings nothing spectacular or revolutionary to the table aside from slightly higher resolution for an excessively higher price. Consumers don't need/want it. Myself included.