This is the kind of thing that happens when groups decide that things like resource management and encumbrance are too big of a hassle. Healers kits are 3 lbs. They take up space. You presumably need them when you are not in a place where you can replace them. But you also need food. And clean water. And ammunition. You can only carry so much. Now you have to make choices. What do you need most?
I find you are only sort of right. We don't track it because in realistic terms, it really doesn't matter.
Let us take a Rogue, with 10 str and 10 con (important for food). They can carry 150 lbs with no problem.
Studded Leather Armor, Rapier, 3 daggers, Shortbow, Quiver and 40 arrows = 23 lbs
Thieves Tools, 10 days of rations, waterskin= 27 lbs
3 healer's kits, lantern, 5 flasks of oil = 16 lbs
That is 66 lbs right there, and lasts for 4 weeks of travel (you only need to eat once every 3 days) assuming you can find water every day.
The roll to forage for food and water is a DC 10 in most settings. A successful roll gives you 1d6+wis lbs of food and 1d6+wis gallons of water. So, a single character foraging can likely feed and water the entire party for at least a day.
The big, actual, problem with encumbrance? It is just irritating to track, and prevents you from carrying mundane tools and being clever. Mostly because the weights are insane for somethings. Trail rations weigh 1 lb? 20 caltrops weigh 2 lbs? Your clothing weighs 3 lbs?
But, if you actually track it or track ammuntion, you will quickly find that it is just bookkeeping for the sake of bookkeeping. 5 gold buys you 100 arrows, that is 100 attack rolls and only wieghs 5 lbs. If we assume 2 attacks a round, 3 rounds of combat, that is 16 combats before you need to spend another 5 gp. And, that actually leaves you an excess, and you could have looted other archers at some point for those 16 combats. Same with rations, same with water, same with healing kit charges.
So it quickly stops mattering enough to pay attention to, because other than running low on water, you can't really get overencumbered easily, or run out food with even a minor amount of attention paid to the rules.