Why are the pictures for Garen, Sona, Vi and Zed anime'd ( on info page ) while the rest are stills?

Dear community,

As a newbie I come to you seeking information. I was browsing the champions tab on the info page when I noticed some of these pictures are animated and some are still-shots. If you click on the animated ones ( Which seem to be for Garen, Sona, Vi and Zed ) a special cinematic plays. I was wondering why. My first guess would be that these champions were/are going to be part of some event and my second guess would be that they are just popular champions. Either way I'd love some insight as to why this is if anybody cares to speculate.

Best regards, Sir Jae Bea.

P.S: cinematic links are as follows...

• http://gameinfo.na.leagueoflegends.com/en/game-info/champions/zed/
• http://gameinfo.na.leagueoflegends.com/en/game-info/champions/vi/
• http://gameinfo.na.leagueoflegends.com/en/game-info/champions/sona/
• http://gameinfo.na.leagueoflegends.com/en/game-info/champions/garen/