Really, why the hell doesn't Camp Vengeance have a 3rd level cleric? ANY DISEASE CAN BE CURED IN DUNGEON & DRAGONS with but a word. It's dumb, but that's the rule.
For just this reason. Most of the narrative tension in D&D can be removed through the use of magic. The reason the game includes these work-arounds is so that those players who don't want to deal with them because they don't find them fun or interesting don't have to. Why else have a 3rd level spell that can bring back the dead? Because some players don't find losing new PCs fun, so the game gives them an out at 5th level.
But narratively-speaking... these outs can really make many stories rather inane. As you and Zapp has said, with the right application of magic or class selection, any tension from "jungle exploration" can be effectively negated. Thus, as DMs we have to make the conscious choice to remove those outs from the game, or make those outs harder to come by.
Case in point, in my two Curse of Strahd games I removed Cure Wounds and Healing Word as spells available in the game because I wanted recovery in Barovia to be more difficult. Now, other forms of healing were still available (Lay On Hands, Goodberry, potions of healing, the Healer feat) so healing could still happen... but this out was more difficult to come upon, and was not as available in as much numbers as it would have been in a regular campaign.
I think ToA is trying to do the same thing. Some spells they say just don't work anymore, and some spells they don't make readily available by just not putting NPCs out there that have those outs available. Granted, they don't do everything for us... because every DM will have different levels of difficulty in mind when they run this adventure.
Now yes, in terms of the full scope of D&D magic (currently in the game because of the "fun" factor and not the "story" factor), not many places "make sense". "Logically" a camp in the jungle would include a couple spellcasters that could eliminate all the issues of exploration and survival... but what ends up being the point of the setting if you do?
To make this campaign different from the others, we DMs all really have to make changes to the availability and power of these outs to help support our narrative.