>>11775518>>11775496These
Also, think about the technological aspect of Gen 1. Not enough data space to see separate item sprites.
Now you might be wondering why, when they changed it to what we know as a Pokéball, did they still keep the sprite the same and encounters such as Voltorb and Foongus around?
That's answered in Colosseum. The items aren't in PokéBalls. They're in chests that are designed to look like PokéBalls.
I know it's missing two Canons, but it makes sense in my head.