The share price of GM, Toyota, etc is based on the concept that they will be able to continue to generate similar revenues and profits in the future. This is not a given.
To survive and prosper, they need to be able to make and sell large numbers of compelling all-electric vehicles at a profit. Right now, they have demonstrated that they are able to make battery-electric vehicles. Debatably, GM has even demonstrated a *compelling* battery-electric vehicle. But the economics are fuzzy - the low production volume and dependence on incentives suggests that all is not well. GM can hide it's floundering EV-programs in the fossil-car revenue, but one day, in the not-so-distant future, these EV programs must support the share price of the company. Is that a transition I would bet on GM executing flawlessly? Not really.
Now, maybe GM will make it, but most likely, there are large car companies that will not. Maybe Toyota or Fiat-Chrysler are in more jeopardy, given their almost non-existant EV-programs. Personally, I wouldn't bet on any of them making the transition successfully, knowing that some will not. The risk in their current unsustainable business models is far greater than my comfort level.
As a result of the above, I feel much more comfortable in investing in Tesla. Tesla is a company that has made the transition into the future, and all the risk now lies in the execution. The execution risks seem managable. Tesla may not always deliver on time, but they are on the right track - not the track that goes off a cliff.