The squarish glyph-shapes aren't a good fit for spaces. Scripts with spaces have unevenly shaped letters so that one can quickly scan a word by its length and

The squarish glyph-shapes aren't a good fit for spaces. Scripts with spaces have unevenly shaped letters so that one can quickly scan a word by its length and pattern of ascenders/descenders. In Japanese spaces do not aid this type of scanning, and conversely the uneven densities of the glyphs allow for fast scanning without the aid of spaces.