What does Atlassian do perfectly? And please don't use the J word.
I'll admit I've not looked particularly hard, but as far as I can tell nobody has a competing product, so Atlassian basically owns the whole field at this time.
There are lots of good modern alternatives to Jira. The reason people still use them is the same as why Oracle DBs are still so popular – they have a large sales team and corporate contacts, and so their products are pushed down your throat.