Yesterday I played two (three as the last one was the bugged flooded arena) tournaments for this emote back to back, and getting thrashed on each of them.
Probably will only play one tournament each day to keep my sanity, and to leave more time for me to do other stuffs.
I'll answer each thing.
1. Why are these tournaments only created by creators?
Probably because it's meant as a way for creators to interact with their audiences, plus having an easier-to-control system (guessing here).
2. There isn't any tournament to play right now?
Yes, there are many active right now, and many more to come.
3. Is it gonna be rare?
It's not gonna become rarer after today, in fact, it's gonna become more common with time. I think it will probably be a bit rare, but it's not going anywhere as far as I know.
Don't panic, this is not a limited-time event. This will be here in a month, as far as I understand, and you don't need to burn out through 100 tournaments today to get it.
It's also extremely hard to get right now because even PROs are going for it. Might be better to wait a bit.