Their pricing model is different, which I think keeps the base feature-set neutered. They try to up-sell you to JIRA and Confluence, which disincentives them from improving the base tools, IMO.
Do we want people to use JIRA? If they require more than simple issue tracking, absolutely. But that doesn't mean that we aren't improving the base tools.
For example, Bitbucket already provides the ability to vote for issues and recently added rendering of the CONTRIBUTING.md file for pull requests (http://blog.bitbucket.org/2016/01/26/pull-request-guidelines...).