These scopes can be useful for stills, but they’re generally less essential there than in video.

For still images, photo editors usually rely on histograms, curves, masks, and hue/saturation tools, which already provide the key information needed for single-frame correction. An RGB parade is somewhat similar to separate or overlaid RGB histograms: it can make channel differences easier to spot quickly, but for a single image it often doesn’t add enough benefit to justify being a core tool.

Vectorscopes are especially tied to video workflows because they help assess color balance and legal/broadcast color over time. Since still photos aren’t made for broadcast and don’t change frame to frame, that kind of monitoring is usually less meaningful.

That said, some still-photo software does offer these tools. Darktable includes a waveform display, and some specialized color-grading tools also provide more advanced color visualization than mainstream photo editors. So it’s not that the scopes are impossible or useless for photos—just that most still-image workflows prioritize other tools that are often more practical for one image at a time.