Glad you asked.
At one time, people were amazed by DVDs. You could put a long movie on it with high quality. Well, that is alright with movies. But if you take a bunch of digital photos, even ones nicety reduced to a piratical size, they will take more space on a DVD that what you would think. About 500 max. As a slide show.
The issue is how people want to use the DVDs. Few, if any. DVD players have a method for showing photos in a slide show. Flash drives solve the problem. Flash drive are not mechanical thugs that haven to rotatable at a constant speed.
Many, even most, new TV sets have a USB port. It is for showing a slide show from a Flash drive. A nice little 4 GB Flash drive can entertain your relatives for about 8 to 10 hours. Whereas the DVD would maybe do 1 or 2 hours. Because the DVD is a movie, not a set of still images. Standard DVD players have no simple way to show frame by frame.
Soon all-in-one DVD players will go the way of record plates. Just buy a new TV with a USB port. It is also like how the PC is dying to the Smartphone. People like things and are small, easy and work better. DVDs are too big. An you have to cover them. Good Flash drives have a MTBF of a;most ten years. Unless you leave them on 24 hours by 7 days a week.
Yeah, I know. Some of the youngsters have never seen a record player and now the are cool again. When my girls were moving into our new a house, they found two 45s left by the previous tenant. I showed they how to use a phonograph. Never mind the lyrics were in French and my girls speak English and Spanish. They played the records overs and over. They memorized the lyrics and could lip sync with the French lyrics. It was cute.
Still, I am sure the DVD is going to fade away in favor of tiny Flash drives.