Hey connorsrpg!
People who want to 'dive right in' to the desert will probably die of thirst
People who want to 'dive right in' to the arctic will probably die of hypothermia
People who want to 'dive right in' to spelunking will probably get lost, get trapped and then then die.
(hell stuff snipped)
The point is, you need knowledge, training/experience and the proper equipment before even thinking of venturing into hostile environments. Hell should be more (physically AND mentally) hostile than anywhere on Earth.
really? Low level campaigns should not be able to be set in such regions? Humans cultures exist in those regions in our world. There is no reason not to support campaigns that take place in those regions or visit such regions at levels 1-10 (in the latter case, maybe, some of the PCs hail from such regions and there is a need to go there or there is some other reason to adventure there).
Having to pick up a supplement with rules supporting levels 11+ which I would probably never use (not a fan of any edition above 10-12- especially, 4e with paragon paths and epic destinies being required) just to get environmental rules would ensure I never pick up such a game.
The same goes for a boxed set to get the other planes like the Feywild.