imagine if people didn't study English. How would people be speaking and learning today? In order to sound educated and literate people need to thoroughly study English. It is also heavily needed in the business world as well as your own private world. English also teaches you to communicate and process things more accurately. If we didn't have a set English language communicating would be extremely difficult.
The main reason to study English is to sound educated and literate. In order to advance in the professional world, you must have proper English and good speech. For example, although President George W. Bush is an extremely smart and important person he at times lacks public speaking abilities. This has been a detriment to him and a big reason why people may not favor him. Where as, President Bill Clinton spoke very well and was very poplar with the people because he was able to properly connect with the public. This ties in the reason for why studying English thoroughly is important in the business world. In order to obtain a good career an advancement as well as respect from your peers you have to be literate and well educated.
An additional reason for studying English is for communication. You are much more accepted in the world if you portray yourself better. People will think of you in a better way and you will have a better chance of being accepted. You will most likely also have more opportunities in life.