Had to read up on this, because it's very interesting.

The short of it seems to be that production runs of Mirasol panels had very high fault rates, which lead to delays and losses. Qualcomm ultimately decided to abandon it and to fully focus on the Snapdragon processors which were perfectly aligned with the booming IoT space at the time.

Mirasol was apparently very promising and ahead of its time, albeit immature. It was based on electro-mechanical mirror pixels rather than dye. The biggest technical downside seemed to have been that the colors were pretty washed out and bland.

EDIT: It actually did make it to market. There was even a smartwatch powered by Mirasol (the Toq). It was never implemented by the big e-Reader brands though.