they're short for practical graphical reasons i think, since they would look really strange if they were as tight as they need to be.
That said, the short versions DO exist, and the male ones actually make MORE sense in that regard, as summer festivals will frequently have men wearing shorter versions while they do things like haul massive shrines or throw fire at things.
I've actually worn one. They're not as fancy, but then again these were issued to EVERYONE
They only make sense during summer, though, and usually in the areas that get REALLY warm like Okinawa or Kyushu.