Why does it have the words DON'T EAT printed on every single package? you don't usually come across such warnings on other products.

Probably because they look like candy, and they're packaged with food a lot?

Even if not packaged with food, these sachects left on the table while unboxing, e.g. a pair of shoes, might entice kids... And it's just easier to print "DO NOT EAT" rather than have separate production lines for "for shoes" and "for food".

Although, from the description, it seems they're perfectly safe (because they're inert) to eat...

I realized this week for the first time exactly why. there was one in my instant ramen along with its other seasoning packets. If not paying attention you could easily be having your noodles with added desiccant flavor.

Also used with food stuff. So just producing one SKU with "DO NOT EAT" saves money and doesn't really hurt in other use.

Your body likes having water inside of it, and doesn't like having glass shards inside of it

The packets look like the little salt packets that come with fast food, and the stuff inside looks kind of like salt.

I'm pretty sure it's just following the rules of the strictest food packaging laws among the places they expect them to end up. In some jurisdictions non-food that is directly inside a package along with food needs to be labeled that way. So they just do em all like that.

It's a choking hazard that is sometimes included in food packaging so it's just to cover the manufacturer since they don't really know what products it may end up in. Silica gel is non-toxic although maybe could cause some issues if you deliberately ate a huge quantity of it.

Before I had kids I wondered this. But it's really telling you to make sure your kids don't eat it.