1. Usually integrated with the Enterprise IDP
2. apps/modules usually are part of the security boundary of Atlassian, meaning little compliance headaches if any.
3. Out of the box scaling of per user licenses since individual apps can't have their own independent user limits, they use the whole Atlassian user count. So, if your customer needs just 10 licenses but their Atlassian suite has 500 users, they must purchase at 500 user cal.
4. Atlassian Jira/Confluence are very sticky at the enterprise level. Yes, teams may move to Gitlab, but most customers prefer to stick to Jira/Confluence.