It's supposed to add you as soon as you make your first bet this season, if you were not already in a league. It could be that this behavior stopped working, in which case, I'll try to fix it!

@JamesGrugett this is undocumented but I remember seeing something to this effect on Discord, right?

Inactive users get kicked out of league to avoid clogging up Bronze with dead accounts.

Commenting so I'd know what's the way to opt out of leagues