Many original PS2 discs contained "dummy" files—gigabytes of blank zeros. Publishers added these to push game data to the outer edge of the DVD for faster read speeds. When compressing a game for a 50MB target, the first step is deleting every dummy file entirely. If a game was 2GB of code and 2GB of zeros, you are already down to 1GB.
: Use a tool like FAT32format to ensure your USB drive is compatible with the PS2. ps2 games highly compressed under 50mb install
What “Highly Compressed” Means