Except their distribution network, reputation/brand value, and marketing reach. And their IP in the non-powertrain components. And their manufacturing knowledge which makes the cars more reliable.

And they can fund the move to electric (or whatever) using existing profits. Whereas any newcomer has to raise money and spend time doing all of these things.

While this is probably the best time for someone to attempt to do those things.. the incumbents definitely aren't starting from scratch.. they still have advantages.