It's coming back by popular demand! The Bell Tree World Championship! After three years, our grand gaming event will return on May 18th with ten Nintendo Switch games to play, both competitively and casually. Signups for the event are now open as explained in the new Bell Tree World Championship 2024 thread!
Yeah, the reason for that is that (I think) Mew's Old Sea Map event in Pokemon Emerald was shiny-locked, meaning that no matter how many times you reset, it will never be shiny. This shiny-locking was left out of the JPN version for some reason.