Atlassian provides a whole gamut of enterprise-geared software development tools, whereas GitHub has only just recently started actively pursuing enterprise accounts and providing the features they want.
In addition, Atlassian's services are spread out across many products, which can increase mobility. GitHub has only one product, so while they probably have many teams working on many features, there is still one product they can push releases to.
In addition, Atlassian's services are spread out across many products, which can increase mobility. GitHub has only one product, so while they probably have many teams working on many features, there is still one product they can push releases to.