There are many reasons facebook won of course. One of the reasons is the user experience. Sometimes, allowing certain sorts of freedom to users is a bad thing. Myspace allowed members to customize their pages. This customization at times lead to interesting, creative and very usable member pages. However, most of the time it lead to pages that were difficult to because the background image had the same color as the type. Or the layout was changed such that the page was difficult to find information.
Also, for years myspace has had problems uploading pages. They’re too slow.
Basically, myspace doesn’t look nice and it takes too long to load. Facebook avoided both these problems at the same time. It doesn’t allow users to customize their pages. This allows content to break through the form of the pages, Content is all users really care about anyway. The page design is simple, clean and standardized, which allows people to see instantly what they are looking for. Also, things that are simple and standardized usually mean faster downloads and less frustration for the user.