Joker: Because it's all...part of the [marketing] plan.
The initial trailers are called teaser trailers because they're designed to do just that: provide you with a little teaser for the film. These are usually just to announce that a film is coming and to start building anticipation, and possibly because filming isn't quite done or there isn't enough film ready to build a larger, more cohesive trailer. This is also a marketing stragegy designed to build anticipation for a much larger marketing campaign to come.
The next trailer is usually much larger and reveals a bit more about the overall plot of the film or the ideas behind it. These may be revealed at/during large events such as conventions or even the Super Bowl as you mention.
Usually a month or two before the film is set to come out, there's a final theatrical trailer that's fully intended to give audiences a more concrete and/or complete idea of what the film will be about in an effort to entice them to see it.
Finally, there are also international versions of trailers that are usually tailored to suit the tastes of the local populace, or to highlight something specifically for them. I believe many later ads for the films Inception and the most recent Godzilla film featured Ken Watanebe heavily for the Japanese market, as he's a huge star there.
The point of trailers is to build interest, and marketing behind films is bigger than it's ever been. Even 10 years ago there were only a handful of websites to view movie trailers on, and before that you were beholden to television or going to a movie theater to see them.
Back in the late 90s when the first teaser trailer was announced for the upcoming Star Wars Episode I: The Phantom Menace, and which films it would be attached to (The Siege and A Bug's Life), people paid full admission price to see these films, then walked out as soon as the trailer finished. I remember seeing news reports about theaters putting up signs telling patrons that if they paid to see a movie just to see the Episode I trailer, they would not receive a refund. This isn't an issue anymore because many of them can be released online at a moment's notice, and in some cases are even leaked online prior to their planned release.
Update: A more recent trend in trailers is to have an approximately 5 second mini trailer for the film that's a super short version of the trailer for the same film shown immediately after.
An example is this trailer for Jason Bourne on YouTube.
The reason for this has to do with how videos like this are usually spread now, through sites like Facebook, Twitter and other social media hubs. Most people will casually scroll through their feeds which now also happen to automatically play video. According to this article on Cinemablend, people tend to only pause for a few moments when they hit a video that autoplays in their feed, so these new short trailers in front of the actual trailer are a new way to capture your attention and quickly tell you what the rest of the 2.5 to 3 minute video is for.