Lifep4 BMS and control
Because converters (both step up and step down) are complex, finicky to design, expensive, take up space, generate noise, generate heat, are sensitive to loading, and are inefficient. Converters aren't magic.
Converters for high power are even more finicky to design, and even more expensive, and large, and generate lots of heat so need large, expensive components.
And for your example with 480 cells in parallel: where are you going to get the huge, expensive, heavy wire to carry all the current?
In other words, why would you NOT just re-arrange your cell configuration so you don't need a converter?
You never want to regulate large amounts of power if you don't have to. Cut out the middleman.