Charizard's popularity is almost exclusively driven by the west because of how the franchise developed over here. There was (and still is) a huge segment of the fanbase that gave up on Pokemon after Charizard left the dex and only came back around Gen 6 or so. In Japan, the series remained consistently mega-popular the whole way through, and their fans grew to love the new Pokemon just as much if not more than the old ones. To them, Zard is a relic - one with history and significance, sure - but he's not that relevant anymore. Whereas in the West, we haven't been able to move past Charizard at all due to our overappreciation for nostalgia and general onions culture
