Honorable Mention #2: Angelic Ascension Meet your new Swords to Plowshares or Path to Exile
Some of the reasons include the availability of the franchise around the world, the consistency of the whole concept and the kid-friendly idea that was completely new and original when it first came out (although it had some similar predecessors)
Pokmon favourites in the palm of your hand
It may not always be advantageous to play more cards (see Why would one want more than 40 cards in their deck?), but why was this restriction added
Overall, the gacha system in Pokemon TCG Pocket leans toward Regular packs with low probabilities for rare cards, creating a challenging experience for completing a deck.
Timetwister wasnt banned at the outset because it isnt quite as powerful in a singleton format, and because in games of Commander, theres often more value in casting a card like Time Spiral instead