When the meta is not well defined or teams do not know what to play, they rely on generalist champions (a champ that you can always fall back on) or the ones that can likely have global presence
After Syndra (lane bully/kill potential) and Ryze, the next champs played in midlane were Corki (good laning/global package), Galio (ult), Orianna/Cassiopeia (generalist), and Taliyah (ult)...the first "meta" champs are LeBlanc/Kassadin ( assassins) and Lucian that have likely being banned
Ryze is a generalist champ (that can assassinate fast if can snowball, even if it is unlikely actually) WITH a global presence (ult), that's why he is so high on teams list right now
It will be interesting to see in knockout stage what is the actual mid lane meta