A value "pulled out of thin air" is still better than "almost certainly zero via bankruptcy". And even if Corvettes rather than Teslas are still on sale 10 years from now, that might not mean any value flows to current GM stockholders.

The most likely discontinuity ahead for GM is a zeroing-out of all current stockholders. For Tesla, there are certain discontinuities -- such as acquisition for technology -- that pay off stockholders even if the nameplate disappears.