The Volt was promised to use the gas engine only for range extending but they ended up connecting it to the drivetrain for highway speeds...
The volt was never popular enough, unfortunately. Right around the time we were looking to buy a new car, and had the Volt high on our list, the retired the product line.
GM will go down in history as the auto maker that had nine lives and blew them all on canceling EV and high efficiency products.
Or their customers, who bought less than 21,000 cars in a year -- I'd cancel that production line too.
I think they just didn't do a good enough job at advertising it. Even the salesmen at the dealers didn't seem to really understand the Volt
I've yet to meet a Volt owner who wasn't fanatically obsessed with theirs (myself included). One common theory for poor sales is that dealers tend to make more on service revenue than the actual sale, and Volts run forever with very little maintenance, but I don't know if that's just speculation. I've heard anecdotes of buyers walking in ready to write a check for a Volt, and the salesperson tried to discourage them and steer them towards an ICE vehicle instead.
GM stopped caring about younger buyers a really long time ago. It's worth remembering that the "bailout" was really a takeover.
GM has a good lineup of EVs now. They somehow don't get recognized for them, but they do. (I own one - the only problem is it doesn't support Android Auto which is enough that I give them a don't buy)