Reasons for WordPress
WordPress is MySQL and PHP based Content Management System. It is open source which means it is completely free and can be redistributed or modified.
Almost 30% websites are powered by WordPress. Because of that, there is large WordPress community, so you as a user can easily find almost anything you want to know about WordPress. And there are plenty of free and paid themes and plugins
The major reason for WordPress is so popular is because it is easy to learn for new users. Also, it is very flexible. With WordPress, you can have any kind of website, from blog to e-commerce or even social network.
When you create post or page in WordPress you do not have to publish it immediately. Instead, you can save it as a draft and decide later do you want to publish it. Also, every time you save post or page it is stored in the Revisions. Because of that, you are able to find some previous version of your post or page and restore it.
Post scheduling is also one of great WordPress functions. It is very useful when you go on vacation or a business trip, but you want fresh website content during that time. You just need to create posts and schedule it for certain date and time and WordPress will publish those posts at the scheduled time.
This listed above are main reasons why people prefer WordPress. If you have other reasons, let us know.