What are some reasons that countries boycott the Olympics?

Answer 1

The main reasons are:

• The country is angry at Another Country who will be there, and doesn't want to be in the same stadium with them.
• The country doesn't want to acknowledge the existence of another country who will be there (perhaps because they consider that country part of their own territory, e.g. China and Taiwan).
• The country is angry at the country who's hosting the games (Germany in 1936).
• The country is angry at the Olympic Committee (IOC), usually because they disagree with the committee on who's allowed to participate on behalf of that country.

A boycott is a protest. They're protesting against someone -- the IOC or one or more other countries. Sometimes countries don't attend for other reasons which aren't a boycott.

• The IOC chooses not to invite them to participate, generally because their governments are obnoxious.
• The hosting country won't let another country's players into their country because they don't think that other country is a real country (They're not supposed to override the IOC's decision on this but not everyone does what they're supposed to).
• The country is disorganized and sensitive to humiliation, so doesn't want to send anyone unless they can make a good showing (Soviet Union in 1948).

Many examples can be found on the wikipedia page for "Olympic Games scandals and controversies".

Answer 2

Yes at least one country has boycotted every Olympics