Wordpress is easy to install if you're already familiar with setting up a LAMP stack. A lot of people who just want to blog are not. It's easy to get running and install themes, but honestly it's almost a full-time job to keep it running right. You have to keep up with security updates and deal with confusing config options for custom domains. wp_config, Apache, and MySQL are not something you can use casually.

Also, performance is terrible unless you cache aggressively, which most people don't because it's a lot of work, even with W3. The nice thing about real hosted solutions is they can handle extra load if it happens.

I get why it's popular. The blogging interface is very good, but trying to setup/maintain a server makes me want to pull my hair out.

It's not the setting up that's hard, it's the fact that Wordpress is still bloated as hell.

Not to mention that Wordpress is a security nightmare out of the box, and even more so if you don't keep it up to date weekly. Its just too much work if all you want is a nice blogging platform.