Prices are too high. Range on electric only too short.
So what you are left with is another hybrid option, and there are plenty of those far less expensive, yet with a record of sales and reliability.
In other words, a Volt competes with various versions of the Prius by Toyota, and comes up wanting.
GM has become very much a market follower, not leader. Toyota invested big money and a long time, selling hybrids at market prices.
GM thought with government help, they'd come into a mature market and peel off the premium price layer.
But my guess is that Toyota's own Lexus brand has earned that status, not GM.