Since they usually stand for the same stuff, why is the c word still considered much more offensive

There are just some words that make you cringe when they are said, same as the m word that's a nasty little bugger too.
Oh and I also agree with Alan as women do tend to be a little on the sensitive side.

Because dicks are big and strong whereas cunts are small and sensitive. ( ͡° ᴥ ͡°)