Why can't you run real-time FMV looking games on your computer? Developers aren't doing it.
Why aren't developers doing it? The hardware isn't available.
Why isn't the hardware available? It's not being produced.
Why isn't it being produced? The ROI isn't there because people are too cheap to buy the latest and greatest hardware available and pump money into development.
So when you ask why it's not there, it's totally because consumers are too stingy with their money. When people quit being such tightwads, start buying the latest and greatest hardware, raising the minimum specs, and quit trying to run Unreal on their Cyrix CPU and other decrepit hardware from '97, you'll get what you want.