As I understand it, the International Olympic Committee prefers to keep mixing things up and having the venue encompass different cultures with each event. Europe, as it so happens, has plenty of countries that each possess a unique cultural identity.
Another important consideration is the political stability and the financial support of the chosen host nation. This would explain why they tend to avoid Africa (though there are some exceptions such as Cairo, most of the continent lacks the resources--if not the desire--to be a good host) and the Middle East (political instability). Most of Europe has historically been both politically stable and financially sound, so hosting an Olympics in a European city generally goes off with little trouble.
because , your suck
Europe
London, England has hosted the most Olympics in the history of the games. They have hosted three. 1908 (I believe), 1956, and of course 2012.
Innsbruck
Athens, Greece, hosted the 1896 Summer Olympics, which was the first official olympic games. Paris, France, hosted the 1924 Summer Olympics. Berlin, Germany, hosted the 1936 Summer Olympics. Rome, Italy, hosted the 1960 Summer Olympics. Tokyo, Japan, hosted the 1964 Summer Olympics. Montreal, Canada, hosted the 1976 Summer Olympics. Seoul, South Korea, hosted the 1988 Summer Olympics. Barcelona, Spain, hosted the 1992 Summer Olympics. Atlanta, United States, hosted the 1996 Summer Olympics. Beijing, China, hosted the 2008 Summer Olympics.
Poland never hosted any summer or winter olympics.
Cambodia has never hosted the Olympics.
Peru had never hosted the Olympics.
The Olympics have never been hosted in Bolivia.
Rio, Brazil hosted the Olympics in 2016.
London has never hosted the Winter Olympics.
Torino has not hosted the Summer Olympics. They hosted the Winter Olympics in 2006.