That's because things which may seems small when considered in isolation - colour palettes, character designs, camera angles, mannerisms, even aspect ratios - these things considered together define a film, and changing even one can cause it to be interpreted entirely differently. And in this case, there's another dimension to be considered as well; the transition from animation to live-action. Even in Dragonball were to be transferred, frame for frame, to live-action, the result would still be very different because of the difference between the two media. Animation inherently lends itself to antirealism and anti-naturalism, whereas in live-action, fantastical elements draw attention to themselves, are more the centre of attention than a sideshow. To portray fantastical scenes in live-action as whimsically as they are in Dragonball wouldn't be responsible filmmaking, and as such, to survive the transition there are some elements which have to be changed. Either way, the final product cannot and will not be approached or watched in the same mindset the same way Dragonball: The Anime would be.