As a resident of Milton Keynes (~30 years) I can remember them being mentioned before I moved here.
The problem now is that many bus services drive around the interiors of the nominally 1km square estates, and I fear people expect transport services very close to their doors. Long journey times reflect these "customer friendly" routes, and getting anywhere within a reasonable time demands the use of a car. On the contrary, the monorail would have used the straightish central reservations along some of the main grid roads, and users would need to walk some distance to get to their transport. Several of the grid roads which were originally designed as straight (and possibly looking forward to a monorail) are now bent as a result of interference from officials who didn't take the long view.