Check Run Reporter is the brainchild of Ian Remmel, caused by his frustration with the lack of reporting tools in many popular CI systems and the realization that GitHub supplies many underused presentational capabilities.
Ian Remmel has been formally working in software for over a decade and, informally, nearly another decade before that.
In his time at Cisco and Urbandoor, he became extremely familiar with legacy CI systems like TeamCity and Jenkins and if you buy him a beer, he'll happily go into exhaustive detail about their pros and cons (to be honest, it probably won’t take a beer). For a long time, Circle CI was his go-to CI of choice, but he now mostly sticks to GitHub Actions or Buildkite.