User blog comment:Nelraye/Lore Discussion: Riot, what happened?/@comment-5035765-20140221200827

The League is a huge spectator sport, so it's really the best place to be if you want to show off your powers to the world.... Which covers Syndra.

Yasuo is there to see if he can find clues to the elder's murder... I mean, you've got much of the Noxian High Command there, so it's the best place for that other than running into Noxus itself

Thresh is there because he wants to be, and looking at the lores of the Shadow Isles champions, the Institute just can't say no to them...

aaaaaaaaaand Lissandra... My best guess is that she's there to show off her power to reduce resistance when she makes her move, like a "Surrender or this will happen to you, too" kinda dealio