While scripting could be used for time-based animations, the preference was to use the declarative SMIL. Scripting support was intended to allow more sophisticated interactive graphics.
Hand authoring complex SMIL animations really sucks. The declarative nature introduces obnoxious limitations, and none of the browsers interpret it identically. I’ve spent hours writing it just to find out it only works in chrome, then spend a few more hours hunting down and finding work arounds for all of the bugs in each browser’s rendering engine.