The piece the author is missing, and why zendesk likely ignored this is impact, and it's something I continually see submissions lacking. As a researcher, if you can't demonstrate impact of your vulnerability, then it looks like just another bug. A public program like zendesk is going to be swamped with reports, and they're using hackerone triagers to augment that volume. The triage system reads through a lot of reports - without clear impact, lots of vulnerabilities look like "just another bug". Notice that Zendesk took notice once mondev was able to escalate to an ATO[1]. That's impact, and that gets noticed!
Our Canadian office managed to convince a couple of team members in our American office that we ran on a 20 hour clock, with 72 minutes in an hour. That was fun for a week.