There are many reasons why English has become so popular. One of them is that English has become the language of business. Another important reason is that popular American culture (like movies, music, and McDonald's) has quickly spread throughout the world. It has brought its language with it.
Is it good that English has spread to all parts of the world so quickly? I don't know. It's important to have a language that the people of the earth have in common. Our world has become very global and we need to communicate with one another. On the other hand, English is a fairly complicated language to learn and it brings its culture with it. Do we really need that?