Because diesel catching on fire is totally unheard of.

On it’s own? Pretty much unheard of. Usually is a leak and something else set it on fire.

Batteries on the other hand plenty of cases where the battery itself was the starting point. Is usually cause by a bad design or external factors? Yes, not saying otherwise.

And tbh Diesel is the worse example you could put as requires either high pressure or a continuous exposure to a flame as you could throw a lit match on it and it wouldn’t set it on fire. Petrol/Gasoline on the other hand…