There are only so many nouns that start with G. Everyone knows all Linux programs must be a noun and an acronym that starts with "GNU" (which is itself a noun and an acronym that starts with GNU)
KDE is not an abbreviation, and not in the same way than XNA is not an abbreviation. Originally it was the Kool Desktop Environment which was quickly dropped not for the obvious KDE Desktop Environment but K Desktop Environment, which kinda makes sense given that KDE replaces 'c's with 'k' all over the place -- such as, to wit, its name as it's a reference to CDE. Nowadays it's plain KDE though.
When they finish the words with G they can just add another layer of recursion and create BIG, an acronym for "BIG Is GNU". And from there go on like a word chain game