Some "highly compressed" files are actually . A 100MB file downloads, but when you run it, the program opens a torrent client or a direct download link that attempts to download the actual 105GB game. You didn't compress anything; you just downloaded a doorstop.
For perspective, standard ZIP or RAR compression typically reduces file sizes by 10% to 30%. Even advanced compression tools like 7-Zip on "Ultra" settings might squeeze a game to 70% of its original size. Achieving a retention rate is physically impossible with current lossless compression algorithms. gta v highly compressed 100mb