because the military needed a fast way for data to be communicated over long distances fairly quickly. the alternative was to physically send disks - and they developed the 'internet' to send this information using the telephone lines. the telecommunications industry cought on, and made their own connections through the telepohone lines, and after a while, started to sell these connections to the public, and the internet has been catching like wildfire ever since.
basically. its a very quick and easy way to;
1. make money
2. communicate
3. waste time
and people like this.