Blu-ray is a movie viewing technology from the future. In order to obtain this technology, one must travel to the future and steal it. This is illegal you know. If Anybody is caught in possession of or using Blu-ray, they will be arrested for illegal time travel. Even if they got it through legal time travel, they will still get arrested.
Blu-ray was first invented sometime in the late 21st century. After it was invented (or before), guys from Sony traveled to the future (or the present, or the past if you are from the 22nd century), stole this technology, and returned to the past (or the present, or the future if you are a caveman). Then they kept selling it until it was the present (or the past from the Blu-ray inventor's point of view). You see, this is why time travel is illegal!
Blu-ray is in every way superior to DVDs, but the government says DVDs are better because they are not illegal. Everybody uses Blu-ray anyways, and all of the police can not arrest them because there are too many. Also, the police use Blu-ray too.