>>42911916A possible reason but we're talking about Garchomp, Cynthia's popularity is one thing but the other reason people remember Cynthia is because her Garchomp was a complete beast and not only is it a monster when you fight it, its also a monster in game (just to say it was the first non-legendary pokemon to ever be banned by its sheer force alone instead of cheesy op abilities like wobuffet in gen 3 speaks to high volumes) capable of shitting on everything and through VGC, it has been a menace all around and you can't forget the part where Garchomp was the recipient of the legendary Pachirisu's worlds victory by absorbing all the attacks while chomp just went crazy on the enemy's team, and despite gen 7 marking the generation where Garchomp was almost UU, it rose again back to the A+ tier of viability (zygarde's ban probably helped in that but i digress).
Garchomp has always been known as one of the strongest non-legendary pokemons and that's why he's a popular mon.