The short answer is: You are not doing anything wrong. The standard DVD disc is LIMITED to that resolution.
If you are viewing the video FROM the timeline, are you aware that you may be viewing how your display setting on PD may be set? Mine is set to 'normal' or some lower setting so I wont SEE a HD sort of preview.
Standard DVD discs, I've learned recently, are limited to a 740(??) x 400(something) resolution. ANd I agree that this IS FAR from a 1080-780 30p version. It looks pretty bad to me too - the 'standard' DVD appearance.
I'm in the market for a dvd player that will accept a flash drive formatted in NTFS format (to allow file lengths over 4GB) - so I can copy produced 1080x780 30p productions onto it(the flash drive) - that I will then take and insert into the usb on the dvd player to play at 1080X780 30p.
I"ll eventually get a burner for the computer that I'll burn/create blu-ray DVDs on but, I don't need to store a bunch of DVD discs - I can copy and play what I want to see, burn a DVD if I want to share with a friend.
Just my opinions and approach.
CS
PD13 Ultimate - Build 3516, WIN 8.1, 64 Bit, 16G RAM, Intel Core i5 4460, CPU @ 3.2GHz, NVIDIA GeForce GT720, Graphics Memory(total avail.)-4093MB
LG WH14NS40 Blu-Ray Drive