Because this data wasn't heavily encrypted or obfuscated, tools like the GM8Decompiler (available on GitHub) could simply "read" this section and rebuild the original project file. The Community Drama
While originally built for Undertale , this tool has evolved into a powerhouse for many versions of GameMaker. gamemaker 8 decompiler link
GameMaker 8 executables are composed of a "runner" (the engine) and a "gamedata" section containing all assets (sprites, sounds, GML code). Unlike modern GameMaker versions that use complex encryption, GM8 data is relatively easy to extract and revert to .gmk or .gm81 project files. Because this data wasn't heavily encrypted or obfuscated,
Never run a decompiler on your only copy of an executable. gamemaker 8 decompiler link