Word processors are great for creating documents with a lot of rich formatting, but all that stuff can be a huge distraction. Code editors on the other hand are amazingly good for writing - the writing where the only thing that actually matters is the content, and not the format.
While it's probably been hashed out and written about a lot by other people, the one thing, the killer aspect of it for me, is the ability to scroll the page down, so that whenever you want, you can always return to that feeling of having a blank canvas to write upon. I really love the blank page, and I love writing on something fresh, and so far, code editors are the only things that I've seen do this. The word processors - think Google Docs, Microsoft Word, etc. - all stop you at the bottom of the current virtual piece of paper you're writing on and won't let you progress until you flow over onto the next page. Now, of course there's hacks around this, including just inserting a page break or two at the end of whatever it is you're working on. However, this has always felt really artificial to me. Plus there's always those page breaks and virtual pieces of paper that physically break apart your writing. It can be distracting.
But to be fair to word processors, I don't think anyone writes their blog posts in them, and I don't think that anyone writes their papers that are meant to be printed in a blog editor. There are always exceptions, of course, such as those that use LaTex for all their typesetting needs (I don't really know much about LaTex other than that it exists and that it is very useful for document formatting, and printing math equations).