Also, there was a disagreement earlier between a Titanfall fan and a user who exhibited an almost neurotic need to prove to him that there was little to no interest in Titanfall in Japan based on weak anecdotal evidence. It's not much, but the week of TGS lots of news outlets were discussing the long lines to play Titanfall, and the general excitement of the game. Here's 2 that get all of the important details:
http://kotaku.com/so-far-titanfall-is-getting-thumbs-up-from-japan-1359751074
http://www.escapistmagazine.com/news/view/130104-Titanfall-Devs-Surprised-At-Japans-Positive-Reaction-to-its-Game
A looping trailer of a game is one thing, but a good amount of Japanese gamers have actually been able to play the game. There were long lines non-stop, which is a much better indicator of consumer interest.
And to address the original question. People are hyped for this game because other people are hyped for it. This game has the backing of well known, and not-so-well-known game journalists, devs, and most importantly gamers! Normal people like you and I, with similar interests. They have allowed the hype to spread and the game has kind of spoken for itself.
Additionally, this game embraces 3 very powerful gameplay pillars and does it very well.
1. Fast-Paced First Person Shooting
2. Parkour, freedom of movement, something that is not done very well in many games, especially not shooters (remember Brink?).
3. Mechs, and this is crazy because mech games are almost as nichey (totally a real word) of a genre as bullet-hell shmups.
It's the combination of these elements, matched with the overwhelmingly positive response from journalists (some of whom have been in the industry for more than a decade, and are literally the human manifestation of "been there, done that) that has convinced people that Titanfall is a pretty fresh experience. Given how different it is from a lot of the shooters we have now, we rarely get the opportunity to be excited for the new generation this soon in.
