I think the biggest reason to
I think the biggest reason to cancel the Volt was that it was a low-margin car (the margins getting even lower with ZEV credits), had and extremely costly and convoluted supply chain, and sold really poorly. It's extremely unlikely that an advertising campaign of any sort would have helped the sales as significantly as the cost of that campaign would have hurt the margins.
The final nail in the coffin is that, for all of the reasons above, it offered GM and customers less value than an all-electric version would.
So the bigger question for GM is what all-electric sedan is replacing the Volt?
To me, all would be forgiven if they were to release a Malibu EV with 300 miles of battery range and 150 kW charging.