The plane acts as a Faraday cage and the skin protects the on-board electrics to a large extent. Why does lighting hit a plane when it's not grounded? It doesn't have to be grounded. It just has to be close to the path of the lightning.

Planes get struck by lightning because they act as conductors that complete a path for the electrical discharge between two clouds or a cloud and the ground. Lightning doesn't need a "ground" to exist; it is simply a massive spark looking for the path of least resistance to neutralize an electrical imbalance. When a plane flies through a highly charged area of a storm, its metal skin (or specialized conductive mesh in carbon-fiber planes) provides a much better path for the electricity than the surrounding air. The lightning typically hits an extremity, like the nose or wingtip, and the current travels along the exterior "Faraday Cage" of the fuselage before exiting at the tail. Because the electricity stays on the outside skin and doesn't pass through the interior, the passengers and sensitive electronic systems are kept safe. In 2026, every commercial aircraft is hit by lightning at least once a year on average, and they are engineered with "static wicks" to dissipate this energy harmlessly back into the atmosphere without any structural damage.