The short answer is that DVD players have been designed to prevent recording.

Music and Video copyright holders believe that recording music and video in your home is a theft of their intellectual property.

It is a complex, emotional issue. In the print media there is a long standing principle of "fair use." The spirit of "fair use" is that, once you have paid for the work, you may copy the work, cut it up, paste portions on your refregerator -- virtually anything -- as long as your replications are for your personal use and are not sold to a third party. The music and video copyright holders reject the notion of "fair use".

There is an excellent discussion of the recording technical and legal issues on the Home Theater HiFi site.

What can a person do about the situation? Write your congress person. Professional help is available at HRRC (Home Recording Rights Coalition).