Why don't I find a site on Internet that explains what items are for?

[Iscah]

I get it that I don't get it, but you don't get it either. I don't know of any game, and I've played a few, that has chests that don't have storage space in them.

New game, new mechanisms. I wouldn't go into any game assuming that design elements from another game must apply to this one - you can use past experience as a guide to what's probably available, but not a guarantee. Read the help text as it pops up. If it hasn't told you about a thing then it probably either doesn't exist or isn't available to you yet.

In any case I'm struggling to think of any game I've played (RPGs mostly) that even has chests as an inventory item.

Don't retainers look like they must be this game's answer to remote storage chests anyway? No other game I've played has anything like them either.

[Limecat]

The materials that come from monsters have always been in a weird place. The drop rates for all of them are really bad, and the retainer ventures to get them only give you 10, yet the recipes requiring them want just as many of them as equivalent crafts with mining and botany materials. To compound this, monsters in the overworld give almost no exp and aren't really worth fighting, so there isn't much of a cushion of these items available on the market from people out grinding exp like you would see in other games.