Like many, I have often fancied the idea of a hardtop, but quickly realised that to get a really nice fit and finish you'd have to make them bespoke to the car, otherwise you'd inevitably end up with big gaps around the doors and a tricky fit to the windscreen.
I can easily see why nobody wants to make them, you'd never be able to charge a sensible amount for the finished product, there would just be too many man-hours involved to get them right.