Why doesn’t Bugzilla offer this or that feature or compatability with this other tracking software?
It may be that the support has not been built yet, or that you have not yet found it. Bugzilla is making tremendous strides in usability, customizability, scalability, and user interface. It is widely considered the most complete and popular open-source bug-tracking software in existence. That doesn’t mean it can’t use improvement! You can help the project along by either hacking a patch yourself that supports the functionality you require, or else submitting a “Request for Enhancement” (RFE) using the bug submission interface at bugzilla.mozilla.org.