Due to following advantages.
- Easy to use and learn.
- Easily expandable.
- Cross-browser support (IE 6.0+, FF 1.5+, Safari 2.0+, Opera 9.0+)
- Easy to use for DOM manipulation and traversal.
- Large pool of built in methods.
- AJAX Capabilities.
- Methods for changing or applying CSS, creating animations.
- Event detection and handling.
- Tons of plug-ins for all kind of needs.