It's not about the coals, well not ALL about the coals anyway.
It allows the sticks to be propped up to expose more of the wood to the air as opposed to on top of each other in a pile, which prevents large areas from lighting up.
Ideal fire configuration is for the sticks to start burning from the bottom with flames slowly licking up the sides.
This arrangement helps produce the clear blue smoke that we all seek.
As to coals production, too large a coal base will raise the cook grate temps and not allow addition of fresh wood until they burn off enough for the temp to drop.
Burning wood produces smoke (with luck clean blue smoke) and coals produce most of the heat and while we need both, the flavor comes mostly from wood smoke, not burning coals.