I also think that it would be super-useful for submission rejection notices to be accompanied by a few brief reviewer notes (e.g. “too much marketing pitch”, “not open source”, “previously presented”, “duplicated submission”, “off topic" etc) to help submitters
to improve their chances in future (and perhaps also clarify any possible misperceptions by reviewers, as the submissions are by necessity brief). As just one illustrative data point, all 10 of my submissions to KubeCon China and US were rejected, and none
of the rejections seem explainable by any of the “how to improve the odds” guidelines. So I have no idea what to do differently in future.