Why can't we move around bookmarks in a video?

It's frustrating that we can't adjust a bookmark in a video on a PowerPoint slide. I often use bookmarks to control pan and zoom in my videos (which is rather difficult and awkward, but that's perhaps another conversation), but if I realize my bookmark is slightly too early or late, then my only recourse is to delete and recreate it. That seems unnecessarily cumbersome. Couldn't bookmarks be made to slide along the video's playback bar, carrying any related animations with them?