I think it is because we already had the traditional Junior (right at the end of its life, however, still on sale) Turbopower Junior as well as the regular hardbox Turbopowers and of course, the Turbomasters...There wasn't really much of a market for it, I don't think and it was still no cheaper than a Turbopower Junior...In many cases, the Turbopower Junior had other features, like the height right control and a headlight.
Another thing was, it wasn't sold in Argos, which is most likely where many people would of bought their vacuum cleaner, it was sold in Index and probably Currys and/or Comet.
It is a shame, as it is a really nice machine.