Just being real here though, hiring flaky employees is enormously expensive. Every hiring manager / business owner would just as soon not waste their time on it. So there are these heuristics that have organically developed for how to spot good employees vs bad. Not having the stability, foresight, or courtesy to (be able to) give notice is merely an indicator of whether you have your shit together. Similar example: an HR director once told me early in my career that drug tests (back when those were a thing) are basically just IQ tests - the company doesn’t give a shit if you smoke pot, but if you can’t control yourself enough knowing you have a test coming up or you can’t figure out how to engineer a workaround, you’re probably dumber than the candidates we want.

The system is reasonable in the sense that it’s explainable and predictable on both sides. Social convention seems preferable to me in this context to binding contracts.