There is always the possibility of deaths by old age; as far as I know, none of us have observed the local elders over the years. If they were brought back to the Pokémon Centers after "death", at some point they'd do nothing but reappear there over and over.

[Which doesn't sound like a very pleasant fate.]

And allowances for products that are simply not available in any shape or form, I assume. I know I've not seen some of my favorites here.

[Johto: the best fitness camp there is.]