All of the information for those multimedia items had to be contained within the multimedia. If animation was involved, the multimeda would sometimes have to include the engine needed to render the multimedia in the correct manner for the animation to work. The simple design of the software was also caused by the limitations of the hardware available at the time. The idea was to keep the rendering software small and simple for systems that were limited on CPU and storage capability. CPU and storage capabilities are far greater now.
Video cards have their own specialized CPU's to handle the demands of high end graphics rendering.
Now, the software on the systems can be designed with less concern about hardware capability. More importantly, the software can be designed to handle more complex and commonly known rendering concepts. It provides a robust set of multimedia interfaces and functions to render anything on the system utilizing simplified commands and data sets. Vectoring is one of the rendering concepts the DirectX implements. Instead of sending tons of data to represent individual pixel attributes for millions of pixels and sounds, the data provides instruction sets that are already known to the vectoring engine.