Why does Pokemon totally dominate the collectable monster genre? Was it already dominant in Japan before being released in the west (Japanese Pokemania?), or is it mostly a product of being the first to the global market? Was it more nebulous, like the mix of cute and cool monsters adding wider appeal than Tamagochi's focus mainly on cute or Digimon's focus mainly on cool? Was it because it hit so many markets so fast? (Game, Anime, Manga, Card Game, Toys, etc.)
Why do modern attempts to make a rival generally fail? Do they all have fatal flaws, or is it just too big a hill to climb to overthrow a series that has been dominant since the 1990s?

Standard explanations for the success of Pokemon seem to basically be: It was released and it was good, so it became a mega-hit. But that seems like too easy an explanation: Lots of games are released, are good, and become mega hits. Few become a mega-phenomenon the way Pokemon did with Pokemania, and even fewer totally dominate their genre for 30 years the way Pokemon does.