By reusing CGI shots, they didn’t have to pay people hours and hours to create new effects, new landscapes, digital frontiers, etc.
Movies that rely on CG effects cost the most to make, that’s common knowledge.
But is this even possible after 20+ years? I can only imagine how many software compatibility issues there’d be, if the files would even be intact after all this time. Not to mention that 1999 CG would probably stand out if placed beside 2022 CG. Reusing film shot I get. Just re-scan it and remove the blue screen, etc. if applicable. But reusing CG that old just seems implausible to me.
Some of those shots were filmed practical or filmed in miniature, watch the special features for The Phantom Menace, lots of miniatures.
These shots were upscaled due to being shot on 35mm film.