That's because DVD 480p quality is actually good enough for most people and most screens. Really big screen TV's don't look great with 480p, but laptops, tablets and smartphones are absolutely fine with 480p. When people complain about not getting 4K on a device that is 16 inches or smaller (laptops, tablets and smartphones) then they are just upset because they know its available -- not because they are really going to notice much difference in video playback.
I'm sure there are a few who can really see the difference in video playback, but they are not the majority of people and are definitely less than the number that claim to be able to tell the difference.
We still playback our old DVD's on our 60-inch TV and nobody notices. I often purchase animated content on iTunes for my teenagers in SD (480p) and they don't notice and we save a ton of money since the SD version is usually much cheaper.
4K and HD are great for some content and some screens, but its not necessary for so much of the content out there and definitely not needed for small screens.