Because your average graphics designer or blogger has no idea what Apache is, what public directories or file permissions are. They just want to run their own blog. That's why Wordpress (or PHP for that matter) is successful; it's easy to set up and get started.
There could be many reasons, not the least of which is that the hosting provider would be providing the installation and updates for the user.
So, they are paying for it by people who are presumably more experienced.
Edit: Just to be clear, I'm not excusing any of the mistakes. Just pointing out how normal people could get screwed over, even if they are using a "professional service" and paying for it.
