Because these files are signed, even if you extract them, you cannot simply modify and repackage them for an unmodified console. Extraction is primarily for analysis, backup, or modding on custom firmware (CFW) or emulators .
You need a tool like or PS3PKGSplit .
Emulators often require games in "folder format" rather than a single PKG file to function correctly.
Over the years, the modding community has developed several reliable tools. Here are the industry standards you should have in your toolkit.