Thanks to dedicated communities of "repackers" and emulation experts, many classic titles have been shrunk down to without gutting the core gameplay. These files use advanced compression techniques (like CSO, GZ, or 7-Zip LZMA) and sometimes remove redundant data or optional language packs.
If your storage is extremely tight, these titles are even smaller but pack a punch: highly compressed ps2 games under 500mb best
Over-compression. Some repackers removed critical file pointers. Try re-downloading from a different source (CDRomance is safest). Thanks to dedicated communities of "repackers" and emulation