new Metabones adapter gives nex crop factor higher-quality full frame look.

A supposedly high-quality product looking for brand-recognition for this growing Canadian company, Metabones. This would not happen if they priced low. The unit includes at least one glass element and is dual-function. If the glass is a good one, this costs too. Plus paying off the R&D. An innovation checking to see what the market can bear, can't say as I blame them.

The Leica R version may be cheaper because it only has one single glass element. Registration distance compensation element not required.

They started with the Canon EF because of the many new NEX-adopters flocking over from their huge Canon DSLR's, who wish to be able to use their old Canon lenses. Good place to start.

Your suggestion of an Alpha mount would put them in competition with all the other third-party Alpha-mount lenses on the market...why should they bother. But you can still buy one of these if you wish.