I don't even think Jira is specifically bad. If someone was only using it for basic project managment and ticketing, it'd be acceptable.
However, occupies the same niche as SAP or Oracle businessware.
First, Take a service that must be ergonomic because people rely on it all day to do their job. Next, make the primary requirement the ability for managment and finance to run reports. Then, outsource it to a company that wants to add custom web frameworks on top of a decades old project. Finally, graft on decades of customizations done by different generations of contractors.
My company had resisted the urge to bolt on additions more than most. We recently migrated from Cloud to on-prem Server as a result of being acquired, and it is amazing how much zippier our project is compared to some of the peer projects that have accumulated cruft.
If you can admin your own Jira instance and keep the fields and plugins to exactly what you need, it's pretty nice. I keep going back to it for the customizable workflows and fine-grained access control.
Unfortunately, every corporate Jira instance I've ever worked with has been overrun with every possible field possible, an unnecessary and constantly shifting mishmash of plugins and horribly slow access. You're paying the price for all of that cruft that you don't need and which can't be removed because "maybe someone wants it."
I've seen multiple different fields for the same value, each of them created for their specific team. The instance is slow AF most of the time due to the bloat and often I can't even assign a sprint to a JIRA because the field doesn't load anymore.