Tesla does a great job of protecting the pack, but li-ion cells will catch fire if crushed beyond a certain point. The anode and cathode in a li-ion cell are separated with a liquid electrolyte that allows the reaction to take place. Crush the cell, the electrolyte gets squeezed out and the two electrode touch. Then all the energy stored in the battery is released at once, creating a lot of heat and starting a fire. It's a weakness of li-ion technology.
Any accident that crushes or rips open battery cells will likely result in a fire. Of the recent Tesla fires I know anything about, all happened from high speed crashes like the Model S that plowed into a tree doing over 90 mph in the Netherlands or the crash in Indianapolis where the car may have been going more than 100 when it hit a tree. It's kind of impossible to maintain pack integrity in accidents that that kind of kinetic energy. Teslas probably have more than their fair share compared to other EVs because they have higher top speeds. I think the top speed of the Bolt is 91 mph and the Leaf's top speed is 93 mph. The "slow" Tesla (currently the 75/75D) tops out at 140mph. The big pack cars are firmware limited to 155 mph.
People want to feel the performance of Teslas and end up doing stupid things.
