Much like with Windows (which takes up well over the majority of computer users!) Internet Explorer is easy, familiar, and user friendly. Making it the "best" choice for many people.
Internet Explorer comes standard on many computers, so it could be laziness. But also, many websites are optimized for Internet Explorer. It is rare, but sometimes there are websites that will not work on any other browser.
Everyone uses internet explorer because it is what is already loaded onto their computer. Many novice users may not even realize they can download other browsers
