Recommended burn resolution & choices smaller than actual

I have my movie video all ready and can confirm that when I go to File > Get Properties For > File > and pick the same file I chose to burn it has an Image Size: 1280 x 720 Frame Rate: 23.976

Then I go to File > Export & Share > DVD and the recommended set Elements 15 picks is Image Size: 720 x 480 Frame Rate: 25

There is only one other box I can choose - Image Size: 720 x 576 and this is so-called "Custom Settings".

Why will it not use the same quality as the original?