I'm not the one maintaining Jira at our shop, but we've got a number of integrations. FishEye for one but also custom stuff like our customer database (so we can assign customers to issues), and in our build process (issues gets updated with built version automatically).

Not sure if those integrations would translate well to the cloud version.

There's also something about owning your own data...

Besides, I found Jira ok enough speed-wise, but judging from all the comments on HN each time Jira is mentioned, the cloud version seems not fun at all.

Business requirements (usually tracing to contracts or law) to have real stewardship over your data.

Not every product domain can operate where they only rent access to the authoritative copy of their records. Or don't have control to acceptance test / rollback the specific versions of the software involved in displaying/modifying those records.

In the past I've worked on safety critical software. As a first order approximation: either the local IT department's disaster recovery plan can ensure continuity of all the quality systems' digital records, artifacts and tools, or you don't actually have a quality system.

Speed (the cloud version is extremely slow and I can't do anything about it, on-prem gives me the option of throwing more hardware at it) and privacy/data protection.