Bootstrap is used for building websites for the following reasons,

☛ Mobile First Approach: Since Bootstrap 3, the framework consists of Mobile first styles throughout the entire library instead of in separate files.

☛ Browser Support: It is supported by all popular browsers.

☛ Easy to Get Started: With just the knowledge of HTML and CSS anyone can get started with Bootstrap.

☛ Responsive Design: Bootstrap's responsive CSS adjusts to Desktops, Tablets and Mobiles.

☛ Provides a clean and uniform solution for building an interface for developers.

☛ It contains beautiful and functional built-in components that are easy to customize. It also provides web based customization.