Well, like the video explains, I think a lot of people don't recognize the problem, because it's less obvious with 24-bit color. And, if they do recognize the problem, they might think it can't be fixed, or they might not think subtle bands are worth fixing.

I've used the following in the past with a lot of success, for one-click fixing Photoshop banding.

http://nomorebanding.com

The alternatives to dithering a 256 color image both end up with undesired results. You can either create a palette specific to your image or application (which makes the rest of a multitasking system look like a tie-dye shirt), or have really, really ugly banding since you have a mere 256 colors to work with (minus reserved colors) instead of 2^24

24-bit images are 'good enough' and dithering would just add another step to the asset workflow.

I can remember the days with a 1MB video card and Windows 95 - switching between 16-bit color at 800x600, or 8-bit color at 1024x768. Resolution vs dithering...

I can't say for sure, but one of my guesses would be stability. By that I mean that the noise is acceptable for a single static image, because it doesn't change - but distracting in an animation if the dithering completely changes from frame to frame.

I might be a non-issue - either not noticeable or not distracting - and the real reason is that people just don't see banding as a problem or that the rendering overhead per-frame is too much.