I'll preface this by saying that humans are terrible pilots[1], but the reality of the problem is much worse than just navigating a quadcopter around on GPS coordinates. Pilots are responsible for a complex decision making chain way before the flight happens. Is the weather safe to fly in (no thunder storms, winds low enough, density altitude, etc. which is not trivial when you're running such a small aircraft)? Is the aircraft in good condition and safe to fly? Is the cargo weight and position within the operating envelope?

[1]: https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?E...