From what I’ve tested I would say that it’s very time consuming. Making sure what processes are being done to the footage are constructive to the shot and don’t take away anything or create unwanted artifacts. Aside from that the SuperResolution tool is very fast compared to the Detail-preserving Upscale effect, however the latter produces better results. That ends up as significant render time for each shot along with whatever you decide to do in addition (Like Denoising, adding grain back and color correcting/grading the footage to match a source).

That is basically why. Or many just haven’t discovered it yet.