I never knew badminton is a thing in gambling. Tennis a little like badminton is a very popular game for sports bettors. I played badminton before especially when I was a kid. During that time, the Indonesians and Chinese were very tough competitors. Now the Japanese, Indians and the Danes are also in the top. Japan Open is ongoing attended by the world's high ranking players.
We have sports lover all over the world who prefers to gamble on different sports and Badminton is also among them but I don't Rollbit have added it to their sportsbook as they have launched with 60+ games (have not checked it recently but to the extent I remember ) so if you are interested in badminton then choose some other option.
People who likes gambling will bet on anything as long as there's some kind of "chance of winning" over others. Just checked the sports betting menu on Rollbit and Badminton isn't a thing there yet, I see tennis, table tennis and squash though, which I think I haven't seen yet or how it's being played.