For the Japanese defuncted competitions, the one I know of like NEC cup, they were having financial issues due to the financial crisis at that time, so their sponsorship stopped. Other smaller competitions got canceled, I think is because their top prizes are too low to attach top players to join, no people watching, no point in sponsored more.
There used to have Korean Meijin, Tengen, etc title match mirroring the Japanese ones, and they got canceled I believe has more to do with Korean Baduk Association internal issues, but not so sure exactly why, maybe they also had sponsor’s issues, someone knows more might help fill in the blank.
And everything goes for the Chinese tournaments, they can be any reason, or no reason, because someone on the top says so. Having said that, the prize for the Chinese Team League is huge compared to Korean Team League and I feel Chinese corporations favor team sponsorship with their name on the team than giving the glory to the players for title matches. And Team League has more games every year and frequently. So pro players also favor that (even some Korean and Japanese pros join those teams as wildcards)
There are many regional tournaments for amateur players as well, they are group competitions that amateur players can get in and win to advance their ranking for their diploma, and you have to pay fee to play. If enough amateur joined, usually they don’t have the financial problem I imagine, most still have some small sponsors for the top winning prize though, if they are the highest tiers.