[sytse]

Because Atlassian makes money on the self-install version called Stash http://www.atlassian.com/software/stash/overview

You get the source code when you buy a license but it is not open source.

[micmcg]

Bitbucket and Stash are different products with different codebases. Bitbucket is written in Python and Stash is written in Java.