Why Does "Will Not" Become "Won't" Instead of "Willn't"?

Most contractions in English are pretty straightforward: they are, they're; he would, he'd; is not, isn't; we will, we'll. The two words join together, minus a few sounds. Put it together, and shorten it up. What could be easier? But that isn't the case for "will not" which becomes "won't" instead of "willn't." Why does the "will" change to "wo"?

Cont... http://mentalfloss.com/article/55232/wh ... ecome-wont