This right here is your answer. The protection on DVD's was defeated very early into the life of DVD's and due to how they are designed they can't be changed without breaking compatibility. Blu-rays on the other hand have a different setup; where they have added High-Definition Copy Protection (HDCP) which is basically a combination of encoded files on the disc and specific software + hardware which is required to decode them. Of course there are ways to still break this protection, however it is more difficult than DVD's.