Who is making these viruses and Why?

Anyone with some knowledge and experience in programming can make a virus.

Many viruses that have been found are analyzed to be poorly written and broken by inexperienced programmers. There have also been some viruses that have shown very advanced techniques that could only be done by professionals.

While a virus author could be from anywhere, many that I personally see tend to come from China, Russia, and other second and third world countries.

Why? In the past, virus authors created their malicious software just for the challenge and fame. Now-a-days, this has greatly moved to a financial motivation. Browser hijackers try to simulate you clicking on links as this could generate some money through advertisers. Other malware tries to steal your personal information in attempts to steal your identity. Trojans can allow remote access to your computer so someone else can use your computer and network resources for their own gain. Many systems infected are a part of a Botnet that is designed to host illegal files without the computer owner ever knowing. Finally, some try to create a problem in attempts to trick some users to actually pay for their software to remove it. There are even viruses out there that will encrypt your data and hold you ransom where you must pay for the key to decrypt it.