> we largely abandoned JIRA and years later the instance got turned off and deleted

Sorry to be nitpicky, but why did you abandon a tool that contained a lot of valuable knowledge? That's not the fault of GH nor JIRA, that's your fault. At least you'd back up descriptions + comments from these JIRA sources.

The team that makes the decision to change issue management systems and not to back up the data is rarely the team most affected by that decision.

You can trivially export your data from JIRA. If the parent experienced a situation where valuable information was lost because the instance was deactivated, that's not JIRA's fault.

I my case it was a different system that got bought out by (I won't say but your guess is likely correct) and the new license terms were unacceptable

Like many tools defending their moats, tools like Jira don’t make it easy to get one’s data out.