Listen, I have a soft spot for the original Yu-Gi-Oh, growing up with it and GX is my fave series out of the entire franchise.
When I was a kid, watching the 4Kids dubbed of YGO and GX, I never questioned how on earth a card game managed to take over the world to the point it's a necessity to take over the world. Technically.
Now, looking at it... it's both terrifying and hilarious.
Okay, let's see how the game is portrayed in-universe: a holographic battle where monsters brawled it out in a stadium.
For anybody, that's gotta be awesome. Even if one barely knows how to play, the way these holographic monsters duke it out has to be a spectacle. Though in this world, you have to be a duelist on some level. Although other jobs still do exist, the card game is a major player. I'm pretty sure if I were to live there, I think I would be a mediocre player but see the matches as spectacles. Come on, my first reaction to Yugi pulling out Exodia is awesome and has to be impressive for the people watching.
Kaiba and Pegasus literally took over the world with their card game monopoly. Kaiba out of sheer pettiness and Pegasus simply because he likes the game. They can even work in conjunction such as Pegasus hiring Chumley as a card designer.
I really have to discuss Kaiba's pettiness and grudge against losing one card game against a kid. While he made good business decisions to shift the focus from arms manufacturing to games and hobbies, it's primarily motivated by his grudge and pettiness.
He is willing to do almost anything to get Yugi and Atem to challenge him. Duel Academy shows this with Obelisk Blue having all the luxuries and Slifer Red barely above the level of homeless. If that doesn't show petty, I don't know what is.
On a side note, Kaiba is nuts because he is willing to break into the Egyptian afterlife just to duel one guy. Over a card game. What a grudge.
I'm pretty sure Mokuba and everyone else who knows him just went along with it, not just because he has money, but because there is nothing they can do to stop him. Mokuba at many points when his life isn't threatened is munching popcorn whenever his big bro does something crazy. Because if my big sibling does something demented and you know you can't do anything to stop them, might as well join them in the ride with food to watch the thing blow up. I'm sure even if Atem/Yami is stone-faced when he saw Kaiba, he's probably exasperated and not surprised at the extreme pettiness and conceit. Probably after the duel, hopefully satisfying enough that Kaiba doesn't pursue the same route again, Atem would probably sigh.
Really, I don't think Pegasus expected the game to take over the way it had. He probably expected to be pretty popular at best but not world-dominating popular that he and Kaiba are the most powerful people in the world of duelists. Heck, Pegasus was open-minded about other games than DM. Look at his treatment with Duke Devlin and his Dungeon Dice Monsters. I'm sure he would be there for Yugi about his dream career as a game designer.
Just to be clear, Yugi in the anime is wealthy as fuck. He's the strongest pro duelist around and world-renowned. He has the controlling shares in Pegasus' company. He's fine and with that money, he wouldn't die homeless. Even if he decided to pursue game-making. I'm pretty sure that's the same thing in the manga-verse too.
By the time of GX, Duel Monsters practically replaced religion, up there with economy and government. The older Princeton bros told Chazz they planned to have each of them be the top professional there so they can essentially rule the world. I don't think Kaiba or Pegasus is interested in ruling the world through the government; they are already making enough money to last them lifetimes. I'm sure they have connections in every part though... Because why the hell not? Kaiba has enough money to build satellites and space stations.
And Kaiba and Pegasus are up there with Pegasus' production of cards and Kaiba's numerous inventions and tournaments. Seriously, those two gotta be the richest guys in the world.
Everyone plays the game and it's the only game. I really want to be kind and say video games still exist but against holograms duking it out... yeah, I don't see video games surviving. I mean I see cards - not Duel Monsters, regular cards like Tarot and the standard deck of playing cards - surviving since those lasted centuries and I don't see it dying out.
That's what made it so sad though. There aren't many options for games except this one game.
A card game that has been an epicenter for major supernatural happenings including deaths.
I mean, Duel Academy has been transported to another dimension! And students chose to stay in the worlds either because they find their true selves or find something there.
And the school just lets it or has no choice since Bastion chose to leave the school anyway!
Seriously, people can enter and leave the school. In the first season alone, there are so many people sneaking in and leaving the island. I wonder just how normal it is that Chazz can disappear for weeks, come back as North Academy's rep, and re-enrolled. Jaden ran away from the school after his loss from Aster and came back with a new deck. We even see in S4 you can ask to drop out since Jaden tried to do that; least we know he got his diploma.
I know I'm complaining about a trivial thing compared to the more insane world of YGO where these guys do questions and scared of the weird but unfazed. Come on, nobody bats an eye when a supposed vampire came to the island. Did weird things happen prior to Jaden's arrival? Do weird things happen to the people of the world in general? Like Jaden's parents did not bat an eye when it comes to Yubel up to erasing his memories? If things like Yubel happened to a normal kid - perhaps wealthy because affording memory-erasing technology is not cheap, given they live in a world Kaiba went to the afterlife and only stayed alive because he has the tech...and Kaiba would love to live in a world where he shows his wealth - then who knows what happens to others.
It's just... this card game wherein other worlds is the center of life and death situations. While it does help them to survive in the worlds, are they sure they should even play these games that people used as such?
However, each entry deconstructs a common trope and the world they live while reveling in the ridiculousness. I can sense the joy in the writing of the world because they know it's insane but they don't care because the world is simply jaw-dropping.
The original series can be deconstructed in the franchise if the characters are original in another series. It doesn't have to be another thing entirely. Cardfight Vanguard deconstructs Yugioh brutally.
The world of Yugioh is ludicrous and silly. It relishes and doesn't care.
Also the dubbed theme songs for YGO, GX, and 5Ds are awesome to listen to. 4Kids may have questionable dubbing but their theme songs are wonderful.