A broader examination would reveal that although the number of English speakers has exploded in the last eight years, the number of English speakers has expanded during the last 300 years. When England became the dominant sea power, then the world's dominant colonizing force, the use of the language spread around the globe. The fact of two successive English speaking empires, British and American, during this time has made that usage universal. However, politics aside, part of the reason for the dominance of English is found in its history -- because England for centuries had been invaded, various lingual influences (Latin, Norse, Danish and French, to name a few) have all contributed to its foundation. During the Industrial Revolution, at the beginning of the Invention Age, new devices were named by English-speakers, but they borrowed from ancient Latin and Greek, "photograph" and "television" (literally "light writing" and "far away sight") being common examples. English has the ability to be both technically exact, yet poetically expressive. That may be the critical reason why it continues to be used worldwide.
Because English has long been the leading 2nd language of much of the world, it is logical that it would continue to be the common language of commerce and industry. It is a fact that more people speak English as a 2nd language as those who speak it as a 1st language. As global communication has exploded in the last 15 years, so English continues its dominance.
One word -- globalization.
The process of globalization has been going on for quite some time. However, this process has accelerated in the last decade or so as the internet has made it much more possible for firms in different countries to cooperate with one another on a variety of projects. Since the US remains the world's biggest economy, (and because other English-speaking nations are rich as well) it makes sense for people in other countries to learn English. This allows them to have a better chance to engage in commerce with firms in English speaking countries.
So, the major reason for this is economic globalization.
Numerous reasons can be cited as contributing factors in the spread of the English language. Communications throughout the world are involving more people from a wider variety of places, situations, and backgrounds. A common meeting point is necessary to facilitate this communication, and the English language has become that tool.
Some parts of human society perceive English as representing a more "successful" language, frequently defining "success" in terms of material possessions and/or accomplishments. Others consider English as the preferred or proper language for use by the educated or refined. As representatives of English-speaking countries or companies come into contact with non-English speaking groups in the guise of employers, aide workers, soldiers, missionaries, etc., the English language may be seen as part of the role model to be attained.