You have to remember that scene parsing is different from the UHD Cache. Parsing is taking the geometry etc. and preparing it in memory in order to render. The UHD Cache is calculating how light will bounce around the scene. So saving and reusing the UHD Cache has no effect on the parsing stage - the geometry still needs to be prepared in memory ready for rendering.
And that does always happen for every frame, there is no way to "save" the parsed geometry (developers would have to say, as I don't know the technical details, but it's entirely possible it can't be avoided because some aspects of what is prepared in memory may depend on what is in the camera view, so for any frame it may be unavoidable that everything gets reparsed; or it could be that there's no way of knowing whether something has changed or not in terms of geometry, so again, everything always has to be reparsed).
