No one would ever suggest lining the bottom of a car with a gasoline tank, fortunately we don't have too because the power density is so high. Hence they can put tanks where a collision or road debris damage are least likely to damage them.
However Tesla needs a stupendous amount of battery to get its range. Hence we get large cars where they have chosen to isolate the entire pack at the floor of the car. They made the choice to dispense with a central tunnel which could hold more batteries, not use the front engine area or any trunk space.
There were to reasons for their design choice, first because of the sheer amount of batteries needed and second because of pack swapping. I don't think the trade off is worth it.
They can use some of the front "frunk" area to have a raised stack of batteries where the traditional firewall is and do similar in the rear. The could have a raised tunnel down the center line and reduce the need of having batteries so far forward. There were many choices available but they wanted swappable packs.
What statistic I want to see is, how many penetration events have their been versus how many fires. How many cells have to be penetrated to create a fire? Is there some flaw that another component is failing during these minor accidents that is causing the fires?