Why? Aircraft are optimized for weight far more than automobiles. Making airplane batteries safer than car batteries would make them even less energy dense than they already are. Add to that fact that cars have a crumple zone built into them, while an airplane AFAIK does not -- at least not one that matters when it crashes into my house at 100mph.

Furthermore, some Tesla crashing on the freeway on the way to Tahoe is unlikely to start a forest fire. But what about some rich yahoo making the same trip while flying their personal electric plane who crashes in the Oakland hills?

These problems are non trivial particularly because every personal electric plane company wants to scale into the millions.