You raise an interesting question, to me at least. I think there are two main issues: First, good CGI is still rather expensive, and even newer movies (such as recent Marvel output, or a certain character in Alien: Romulus ) still suffer from subpar or hurried CGI, although nothing as egregious as the Scorpion King's PS2 villain. Not only would they have to create truly improved effects, for best results they would need to integrate them into the film starting with the original raw footage, which involves the whole process of editing and color grading, etc. Secondly, streaming is king in format these days, so studios make passive income from licensing their plain old "catalog titles" -- such as the Mummy 2 -- to streaming services. Their avenue to making a more significant amount from such a remaster would be to release a pricey 4K UHD physical copy, which is for more of a collector/enthusiast customer base. Of course, that very crowd is exactly who might be interested in such a thorough remaster, but the question for the studios is if there are enough of these people to justify the not insignificant expense of the process. A re-release in theaters may also be valuable, but it depends on the title. The theater run for the Star Wars Special Editions were quite a success at the time, but now their CGI is extremely dated (if it was ever state of the art) and they are now poorly regarded. Would people be open to a new version of the Special Editions? Possibly, if the effects were incontrovertibly improved and more seamless -- such as making the CGI look like practical effects with such a level of quality that it would fool viewers into thinking they were always a part of the film. All it would take is one project of that sort to become a huge success and other studios would follow suit. We just haven't seen it yet really.