Why do they have left handed guitars? There are no left handed pianos, drums etc.?

Au contraire, my friend; Left-handed pianos are rare & expensive, but they exist, so left-handed pianists simply teach themselves to play a regular piano. Left-handed drummers typically just arrange their drums in the other order.

Some left-handed guitarists, it's true, simply play their guitar upside down....Jimi Hendrix, for example...

Ever try hiting the chords you want on the fret board with your unnatural hand. Takes twice as long to learn then just turning the other way around and let you creative hand I.E in this case the left hand do its magical thing.

drums/pianos require 2 hands......

so do guitars but not to the same exstent as the other 2

EDIT

below...now i never knew that....thanks for the info.

uhh, because pianos and drums have two hands a.s.s.wipe!!