There's something like 170,000 car fires per year in the US. It's just one of those things that's bad and too common to really make the news except maybe locally.
Why? You can do both, if you want to. If a car can’t have good occupant safety, I would find it very difficult to believe its pedestrian safety would be good instead.
Then why doesn’t every car score top ranking on the safety tests? It’s not a “solved problem” if you don’t spend the money/effort to solve it. And it absolutely costs money to solve the problem, which a cheaper car may not wish to spend.