I'm a consultant, and it happens that hardly any of my clients use Jira. So this is the result of scratching my itch (and the itch of people who already give me money) first, and dressing up the result for others to use.
Lots of people have expressed interest in Jira integration, and that's definitely on my list to accomplish one way or another. The Atlassian marketplace is like most app stores, though -- if people already know your name, it's easy for them to find and install your app. But if you're a relative nobody, there are 50 other estimation apps, and very little room to pitch what makes you unique.