Why do engineers hate Jira?

Probably the majority of any hate has little to do with any specific software and more to do with the general concept of trying to have business people assert any kind of authority or set any kind of goals at all, and hatred of such attempts may get transferred to the software by accident.

Relatedly, specific attempts at enforcing certain business-centric processes like Scrum and Agile would be upsetting for the same reason, and for the additional reason of requiring bureaucratic overhead and social interaction, which engineers want to minimize at all cost.

Businesses wishing to enforce such things is completely understandable from their perspective, and the continual search for some kind of workable process is an iterative thing. But probably those places that lean very heavily on the side of process and surveillance have gone too far. Setting and meeting medium and long-term objectives would be the thing to optimize for, instead of obsessing about process or ultra-short term task items.

Because of the ridiculous workflows that many companies use it to impose on teams for no good reason. Also, the API is atrocious, slow and poorly documented and you DO NOT want to know what some government orgs are using it for.

A lot of the hate for JIRA from what I've seen is in terms of its performance, time taken to load a page, for example. I bet it's not just the speed though. I'm curious to know if anyone could share more details.

I don't hate it, but given a choice I wouldn't use it. It's not very intuitive. I felt like I was wasting time trying to deal with it, and never exactly sure why it wasn't working, rather than getting stuff done. My next project used Trello (only for Kanban-related activities) and I was much more productive.

Jira is frankly just bad software. It's unintuitive, proprietary, vulnerable software.

They made it as a replacement for Bugzilla, but for everything it competes with Bugzilla on, Bugzilla wins.