At the minimum it's another account you have to register. The more Jira-specific problem is that making drive-by issue reporting frictionless is an extremely low priority for Jira (or for the people who choose to use Jira), and there's often going to be a bunch of confusing steps required.
It also just signals that they aren't really that interested in hearing from users. People who crave feedback and bug reports go to where the users are rather than making the users come to them. Even if they use Jira internally, they'll do things like monitor stack overflow and provide support on Github.
