Carrying capacity, food rations, and ammunition supplies are not really modular aspects, but integral parts of a greater system that also includes wandering monsters.
Any supplies carried into the wilderness and dungeons slows the party down, which leads to a longer adventure, and as such increases the number of encounters. If wandering monster encounters pose real threats, provide little reward, and consume more supplies than the party can gain from them, then managing their equipment becomes a balancing act that is constantly going on the entire time the players are playing the adventure.
Once common consensus said that random encounters are stupid and GMs first decided to only have one encounter per journey (to get on with the prcious story), and eventually no travel encounters at all, the time pressure disappeared, making encumbrance, rations, and ammunition all irrelevant in the process.