1) Because investors with too much money in their pockets believe the self-driving hype. 2) Because GM (and Ford and Chrysler) has a lot more unknowns and risk

1) Because investors with too much money in their pockets believe the self-driving hype. 2) Because GM (and Ford and Chrysler) has a lot more unknowns and risks given its increasingly outdated dealer-based sales channel, along with decades of pension liabilities, and is ultimately in a precarious situation, see: the near collapse of the US auto industry in 2008. 3) Maybe most importantly, investors believe that ultimately Tesla will be purchased by a big tech company with money to burn (or by a traditional automaker in full panic mode). Apple could pay _cash_ for all of Tesla's outstanding stock and still have the biggest cash stockpile of any corporation in the world.