Why does Yugioh have a ban-list?

Well we know exactly why the Yu-Gi-Oh ban list was invented.

In 2004 a strategy known as the “Yata Lock” was discovered.

All you need for this strategy was to have a Sangan or Witch of the Black Forrest on field and a Chaos Emperor Dragon - Envoy of the End (CED) in hand. You would then summon CED and activate its effect to destroy all cards on field and remove all the cards from both player’s hands. This will activate Sangan/Witch’s effect letting them search for Yata-Garasu. Yata-Garasu’s effect is that if it inflicts battle damage to your opponent they skip their next draw phase. Since you have cleared both their field and their hand, you can keep poking your opponent and effectively lock them out of the game.

Konami decided that this was a problem so they created the ban list to stop it by banning Yata-Garasu and it has stayed banned ever since.

The role of the ban list since has usually been to help contain problematic cards as well as regulate the state of the game.

See Yu-Gi-Oh as a TCG has two unique-ish features (some other card games have these features but Yu-Gi-Oh is the only one as far as I know that has both):

• Lack of set rotation - This means that all Yu-Gi-Oh cards from any period (excluding cards on the Forbidden and Limited list and with special exceptions such as certain prize cards) are legal all the time. You could take your deck from 10 years ago, take out any banned cards and play it tomorrow in a tournament. This also stops the format from self regulating by letting problem cards/strategies rotate out of the format.
• No resource system - Yu-Gi-Oh unlike games like Pokemon, Magic: The Gathering and almost all other TCGs doesn’t have a resource system such as mana or energy. This means that other than Yu-Gi-Oh’s built in 1 normal summon per turn or card specific restrictions it is extremely easy to empty your entire hand on to in a single turn, create infinite loops or abuse powerful effects.

When you combine these features it creates unique problems that only the ban list can solve such as:

• Broken combos: Much like the above case of the Yata Lock it happens that in Yu-Gi-Oh that when a broken or poorly balanced card comes out to create combos that will win you the game (or fictionally win you the game) without even giving your opponent a turn or a chance to respond. Through out Yu-Gi-Oh’s history there have been many decks that could only be stopped by banning one or more parts of the combo such as Frog FTK, Monarch FTK, Firewall FTK, Elma Loop, etc.
• Preventing Stagnation: Players get bored if all their games feel the same so the ban list is a good way of injecting some new life into the game. The ban list can be used here to hit the best decks and either bring down their power level to create space for new decks or it can simply kill the top decks creating a void for new decks to fill. In 2019 Yu-Gi-Oh was in what players were calling “The Eternal Format” where the best decks of the format were the same for about a year and a half with only one new deck coming into the top tier of the format in the entire time. Konami killed all 4 of the top decks simultaneously to force a change in the competitive scene because if they had not those decks would probably still be the best decks even now. Without set rotation to force decks out of the competitive format the only way for Konami to force a change is to ban cards or introduce massive power creep.
• To create diversity: Sometimes Konami makes such powerful generic cards that almost every deck will play them which causes the format to become very samey and leaves very little room for creative deck building. Pot of Greed is one of the most famous cards in Yu-Gi-Oh and has been on the ban list for forever simply because its effect is super powerful. If Pot of Greed was legal in any amount then every deck in the game would play it at that number. This can also been seen in the current metagame where thanks to Predaplant Verte Anaconda any deck that can put 2 monsters on field (which is basically any modern deck) can summon the extremely powerful Red-Eyes Dark Dragoon. So now almost every deck plays a Dragoon package and summons Dragoon either as its core boss monster or to make an already powerful board even more powerful. The only way for Konami to deal with this problem is to ban either Verte Anaconda or Dragoon.
• To protect future card design: There is a well known card in Yu-Gi-Oh called Snake Rain which lets you send 4 reptiles of your choice to the graveyard. This would be an absolutely broken card if it wasn’t for the fact that there are no good reptiles to send to the grave with Snake Rain. Most players suspect the reason that there are no good reptile decks is because Snake Rain exists. Because cards never cycle out of rotation it means that any good card could become a problem in the future especially if it is very generic and thus the card designers have to constantly work around the existence of all 10 000 cards currently in the game. Sometimes it is much easier to ban the offending cards to free up the designers.

So Yu-Gi-Oh has a ban list due to particular design quirks that mean cards can often become problematic and the only way to fix the game is to ban those offending cards.

Source: quora.com
Credit to: Eric Backeberg