For the North American market, largely bercause of several reasons:
1.It would be limited to ATSC (which not everybody uses), QAM (which there is no guarantee or poularity for), or recording component form an STB, which would add some costs for an encoder.
2. Such a recorder might start at $500 on US market, and media at $15 in quantity. It would economically be unfeasable for many, compared to buying the commercial Blu-Ray.
3. The studios would not be too enthused with them, so likely force manufacturers to limit their functionality to sut the interests of the studios to sell their Blu-Rays, rather than people collecting "free" libraries of their movies and TV shows.
4. People are getting their content on demand anyways, or storing it on HDDs, as most of the content collectors I know of are.
5. Optical media is dead.