With the nerfs to the latest build where a) the Brawny talent only reduces the fatigue penalty by 35% and b) you incur fatigue penalties for carrying extra items even with Bags and Belts, we need more inventory capacity. The only real advantage we have in fighting the various denizens is bringing the right weapon to the fight. But with the variety of enemies, an increased roster, food occupying inventory slots, 99 slots isn’t enough anymore.
Also consider that since we now have multi-wave fights, we have the option of swapping out armor between stages but only if we have armor in our inventory to hold extra armor.