The problem with SVG animation is it seems to be abnormally resource intensive. I noticed it on a project I worked on recently -- simply pulsing a few <circle>s larger and smaller pegged a CPU core at a constant 40% on my work machine. Indeed, opening your (very cool) 404 page shows a constant 30% CPU usage.

Fine for a 404 page which people are unlikely to stick around on, not fine for a screen that someone is going to spend a significant amount of time on.