Why is Spotify not available in some countries?

In order for Spotify to launch in new countries, it must acquire the license for the music it will play in these countries, which takes time and isn't always an easy thing to do.

Spotify is working on launching in new countries one step at a time.

Some countries are not considered a valuable market for Spotify to launch in which may be due to political unrest, civil wars or religious reasons.

Spotify has to consider how profitable it would be in the countries it wants to launch in terms of whether people would pay for ads or become premium users. (See Why Album Sales are Down?)

Some countries consider piracy the main source of downloading and listening to music, which means Spotify might not make money in them. 

Developing countries and war-torn countries are not a target for Spotify since music may not be popular or considered important in them. (See Why is Egypt a developing country?)

Countries with weak internet connectivity will cause problems for Spotify and its users, which could be why Spotify doesn't launch in them.