Well people can be hard to replace thanks to skills and training they received on the workplace... which they can quit on a short notice if they are offered better pay elsewhere, causing enormous problems for business owners. So it kinda checks out.

Obligations shouldn't be one way, they should be mutual. If you want an ironclad employment security, etc, etc, you should also accept to be bound to your workplace until the business hires somebody else to do your work who is as qualified to do your work as you are. And if you think that your obligation is only to work well until you decide to quit at the moment of your choosing... then you should also accept that this moment might be chosen by your employer.