Faster mirrors have a range of potential problems - they take an enormous amount of time and skill to make compared to slower ones (ie. are much more expensive), need a coma corrector (a new design is needed for beyond about F3.5), have much smaller collimation tolerances and the diffraction limited field of view is much smaller.
I don't know if they could ever be produced on a large scale.
But, this mirror has allowed me to get fantastic views in a convenient package without a tall ladder - so I am happy!
