Latin and Greek letters were often carved into stone, which influenced their form. Kanji and Hanzi are traditionally painted with brushes, which is why there's such a variation in stroke width.
The main reason the number of Japanese fonts is proportionately low is because there are so many characters that need to be individually designed. Latin alphabets have a much smaller character set, so it's easy for even casual font makers to crank them out. Other writing systems like Korean are very modular, so a small number of elements can be configured to create their characters. Japanese has not only two visually distinct syllabaries in addition to punctuation, but a couple thousand kanji to draw. This means that making a font is extremely time and labor-intensive. But there are foundries out there making quality Japanese fonts, like
FONTWORKS | フォントワークス