Well let's look at what we've got over the years in terms of cinematics:
2009: Trailers for the game.
2010: The season one cinematic.
2011: If memory serves the unreleased Dominion cinematic was at this time? I'm almost certain it was here.
2012: Er...nothing. There was no cinematic of any kind in 2012. I could be wrong, but as far as I remember there was nothing.
2013: A Twist of Fate was the obvious one, but we also had Road to the Cup and Get Jinxed later down the road, and from here we see a new pattern emerge...
2014: There was of course A New Dawn but also Vel'Koz: First Contact, Trials of the Poro, the two Shurima videos, the Harrowing video, Kalista: The Pledge and The Terror Beneath. Pretty damn rich in cinematic experiences of varying kinds.
2015 The Curse of the Sad Mummy, Bard: Mountain, Ekko: Seconds, The River King, PROJECT: OVERDRIVE and all the Worlds Cinematic things with the crystals and stuff.
You might say to me "But Sharjo, that's not what I'm talking about!" well it kinda is in that these are ALL cinematics, just of varying kinds. Just because we haven't had a cinematic in the style of A New Dawn and A Twist of Fate doesn't discredit the others, and I understand the desire for a big mashup cinematic, but in all honesty I prefer just having a crap ton of cinematics that are all cool in their own right.
So to summarise: cinematics haven't gone anywhere, in fact they've came, seen and conquered for the most part, with way more of these cool visual promos being showcased throughout the year that are related to multiple facets of the League of Legends experience, from competitive to skins to lore to just being damn awesome. Just because there hasn't been a champion vs champion mashup cinematic in 2015 doesn't mean much in the scope of cinematics as a whole, considering that since A Twist of Fate we've been getting a crap ton more than ever before.