I also don’t get the hate.
My theory is that, because it is often self-hosted on-prem, some orgs under-provision the hosting and end up with a really sluggish instance, but at the companies that I’ve worked at it has always been quick. Maybe someone here can confirm or refute that theory?
I've had to use Jira Cloud, hosted by Atlassian themselves and presumably meant to be their hosting showcase, and it still chugs and is sluggish once "configured" for a large enough team or the whims of enough managers above that team. That Inner Platform Effect of Jira's weird scripting languages and SQL-like-but-not-exactly SQL filters provides a lot of room for management to slow everything down on every page forever.
Talk to people who have admin'd it instead of just users and you will understand very quickly there are a host of issues. Even with tons of hardware the software is just bloated and slow (tons of reports of "I threw a big system at it and payed for on-prem and it's still slow as cold molasses), the backend/api is atrocious, the tooling isn't foss (who customizes versioning?!), migration is another level of PITA, etc, etc, et al
