Here's why it's not considered the worst:
* It has a specific niche: While not very good, it can be used in specific decks that rely on summoning monsters with low attack and defense.
* It's not completely useless: It can still be used to tribute summon stronger monsters, or even be used as fodder for Synchro Summons.
* It's a meme: Its bad stats and lack of effect have made it a popular meme in the Yu-Gi-Oh! community, often used as a joke.
There are many cards that are objectively worse than "Rare Metal Dragon":
* Cards with no effects: These cards have no abilities and are essentially just there to take up space in your deck.
* Cards with extremely low stats: Some cards have such low attack and defense that they are practically useless in a duel.
* Cards with convoluted or difficult to activate effects: These cards can be difficult to use effectively, making them a liability rather than an asset.
Ultimately, the "worst" card is subjective and depends on the context. While "Rare Metal Dragon" may not be the most powerful card, it has its place in the game and is a fun card to use in casual play.