The nerfing of spells and magic items made to make supply relevant is definitely the aspect of A5E I like the least, and by a lot. IMO it feels very gamey and shoehorned, and creates a lot of conundrums especially with higher level spells.
I'd rather make those "problematic" spells and magic items much rarer and more expensive, but keep them working as in standard 5E.
If that's not option, one could explain the lack of life support as: "Carving out a personal pocket dimension from any plane is a complex and dangerous task, since it requires to take that bubble of space away from some Entity that might claim domain over it. It is much easier and safer to carve out these artificial pocket dimensions from The Void. This also ensures that no entity can enter the pocket dimension uninvited. However, the side effect is that life-support in the pocket dimension is dramatically reduced. While air and temperature can be kept to reasonable living conditions, anything else will provide no sustenance: food will lose it's nourishing properties very quickly and expire much more rapidly, and the connection of living creatures to their souls becomes very faint and fragile"
