Since several other popular trading card games, like Pokmon and Lorcana, use this card size, its known as standard size in the industry
No-Symbol Sets (Early Years): How to tell Alpha vs
Folks saw it as a threat in a similar way to Ayli, Eternal Pilgrim
Tag Team GX Pokemon also were the first consistent implementation of Special Art variations of the "Full Art" Rarity which thankfully was cleared up by the end of SwSh
You can get card sleeves, playmats, coins to show off your style, and repeat cards can be turned into Shinedust, which can then be spent to gussy up your cards with custom animations and the like
To get Pokmon cards graded, collectors simply send their cards to companies such as PSA and CGC, who will then rate the TCG collectible's quality with a grade