Because every Dev/QA/Test team is a unique snowflake. JIRA tries to be all things to all people, to support all the mutant chaotic psychotic use cases, so it becomes nothing to everyone. Just like the enterprisey CRM, ERP, etc systems we all hate so much.
I had high hopes for FogBugz; I like that it's opinionated. But I haven't yet had the juice to procure it. (Atlassian won the marketing mindshare battle.)
Next time I'm in charge of QA, I'll be rolling my own tracker, again. To better support our workflow directly.
I've long wondered what a WYSIWYN tracker would look like. Maybe a HyperCard and wiki hybrid with a versionable schema (to reduce costs of change, because all processes evolve if permitted). Alas, I haven't had the gumption to make such an elegant beast.