Are companies really REQUIRED to post a job posting when they will automatically hire internal candidates?

I've had a couple interviews where I don't get the job and they tell me they've hired an internal candidate, usually because they are already familiar with the policies and procedures. When I complain about it to people, they tell me they are required to post a job announcement. Is that actually true? I just get frustrated, because I've been told I interview well, but if you're just going to pick an internal candidate, why are you wasting my time and getting my hopes up if you're just going to outright take an internal candidate!? To be fair, I do understand why you'd pick an internal over an external, but why not just make it an internal posting?

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