Atlassian products are very complex. Jira alone has sophisticated low-code automation, extremely thorough templating for projects, a rich API, extensive support for i8n, meta-projects (Jira Plans), an add-on marketplace, and so on. Confluence is pretty amazing too when you really understand what it can do.
Edit: Jira’s tight integration with GitHub and ability to drive/be driven by GitHub actions is also a big deal.
Edit: Jira’s tight integration with GitHub and ability to drive/be driven by GitHub actions is also a big deal.