If internal, "hidden", policy is different from public, written, policy...the company can go fuck off.
Professional courtesy would be telling someone you want/need them for the next X months and making a real commitment to the worker instead of having a public policy of 'no obligations' while secretly expecting the worker to 'be a professional' and to show undue loyalty.
It's called "politics". And it occurs when two or more humans get together. There are always hidden agendas, different goals, etc.
Learning to navigate it is an essential prerequisite if you want to accomplish something that requires more than your singular individual skill.
And, for your information, yes, people like you wind up on the short end of the stick because you ignore politics. People like me get new jobs, better opportunities, advance warning, etc. because I have helped out people in the past. The combinations of being both technically qualified and politically savvy is quite powerful.
You don't owe any loyalty to a company, but if you piss off the people, it will bite you in the ass.
Professional courtesy would be telling someone you want/need them for the next X months and making a real commitment to the worker instead of having a public policy of 'no obligations' while secretly expecting the worker to 'be a professional' and to show undue loyalty.