Hi D1omedes,
I've carried many that for one reason or another never went into production.
The development of a model, requires focus and is time consuming. Selection of a collaboration design is the same. Refinement and engineering bring new challenges, and then tooling increases the investment.
Deciding what models our customers will enjoy and appreciate is not a simple choice of "what do I like?". Some designs are ahead of their time, or behind the curve. Some have a very small market and we cannot regain our tooling. Some designs we decide need a lot of improvement and our design, development and engineering time is not unlimited.
For that reason, thee are many prototypes sitting around in drawers that might be considered in the future.
Hope that helps.
sal