Adoption of technology

There are many cases where "superior" technology is not adopted, and there are innumerable failed corporations and startups, penurious inventors and frustrated investors to prove it. While the public may believe "If you build a better mousetrap, the public will buy it," the truth is rarely so simple. (Incidentally, scientists and artists are insulated from these messy but crucial problems of adoption of technology.)

There are many reasons why the "superior" concave mirror (if indeed it was "superior") might not have caught on or been adopted by early Renaissance painters:

1. Ignorance: The artists might never have learned of the existence of concave mirrors. After all, Hockney argues that there was a "conspiracy" to keep the "secret knowledge."
2. Poor advertising/sales/distribution channels: It might have been difficult for mirror makers to bring their goods to market.
3. Insufficient capital: The convex mirror in the Arnolfini portrait was a rare and precious item, included in the portrait to indicate Arnolfini's great wealth. While some painters with patrons may have been able to afford such a mirror, many others might not have been so fortunate.
4. Slow learning curve and high opportunity cost: Artists might fear that it would will take too long to learn this new method and that during such time competing painters might secure the next portrait commission.
5. Poor compatibility: Artists who also wanted to paint ceilings and murals would have been reluctant to embrace the technology.
6. Higher risks: An artist might fear relying too much on mirrors lest it break or be stolen. Of course, there was also a severe fire hazard for those artists who preferred to work by artificial illumination.

What these considerations actually imply is that "superior" technology must be judged on a broad range of cultural, economic, political and legal criteria -- criteria the theory's proponents have not considered adquately. It is very easy to counter the above points in theory, or in an ad-hoc way, but in practice they can arise in innumerable unexpected ways and can be amazingly frustrating.

Summary: Even if it could be shown that in theory the use of optical elements for painting was "superior" to "eyeballing," there are numerous hurdles to the dissemination and adoption of such technology.