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...
Not always, a bad design/construction of a battery I wouldn't call it external factors.
It doesn't need anything external to set on fire.
But I agree that it's not common.
On the Diesel/petrol case.... it would need a leak to begin with and usually it's not s difficult thing to design a tank/engine without leaks. Let's be honest a battery is a more complex system to fuck up.
Yes, there have been recalls as well in some cased.
Here there is info about incidents, althought not only due to internal faillings alone, there are crashes and other stuff as well.
The usual issue is that a thermal runaway happens.