Pitch: "We need some filler Pokemon. Like, something we already have a design for that's incredibly simple, but with eyes or whatever. Oh, I know - we already have all these Pokeball sprites. Why not just put some eyes on 'em and call it a Pokemon? Hell yeah."
I would say the odds are pretty good that someone realized that every item was represented as a Pokeball, but it might be good to surprise the player every now and then by having the item turn out to be a Pokemon in disguise. But to make it almost make sense, they decided to have a Pokemon who just happens to look just like a Pokeball. They didn't bother to think "oh, this is really, really dumb." I don't think it's any coincidence that this Pokemon's signature move is "kill itself." Even Voltorb knows it probably shouldn't exist.
How Lazy Is The Name: The name 'Voltorb' is actually pretty good - 'volt' as an indicator of its electric-type attribute, and 'orb' because it's a spherical object. Really, it's half-way decent name is the only thing keeping this thing from the #1 slot.
1. Mr. Mime
Pitch: "I saw a mime once. What if that human being in make-up pretending to be stuck in a box was a Pokemon?"
Mr. Mime is basically a person. Just a regular person. Not an animal, not an inanimate object, not a made-up thing. Nothing implying supernatural powers or abilities that would be useful in battle. A human entertainer. It's hard to imagine someone at Nintendo hadn't just seen a mime outside and said "eh, that guy could be a Pokemon."
How Lazy Is The Name: Here's the issue - Mr. Mime and Jynx are both very lazily-designed Pokemon. They're both pretty much "people who are Pokemon for some reason." But Jynx at least makes an attempt to be something more with the design and ice-type implying connections to some supernatural folklore stuff. Mr. Mime doesn't do that.
But worst of all - IT'S ACTUALLY NAMED "MISTER MIME." It would be impossible to think of a lazier name than this, because it even sounds like someone desperately trying to think of a name at the last second and coming up empty. "Mister...Mime?" Hell, even calling him "Mimey" would have been better.