I had a buddy, who develops video games as a hobby, complain to me today that the maximum texture size supported by (most if not all) video cards is 2048x2048 pixels.
Do the math, that's 2048x2048x32 (RGBA). That's 16 MEGABYTES in a single texture. My first computer was a Commodore 64, with 64k of RAM (natch), you'd have to disassemble 256 Commodore 64s to get enough memory to store that single video texture.
Hell, the first computer I programmed Hypertalk on had 4 MB RAM, and Hypertalk ain't quick to start with.