Interview Questions for Employers

This might come across as rude, but shouldn't you have asked these questions before interviewing people? As the interviewer it is kinda your job to know this.

This is well-intentioned, but kind of misses the point. The interview process at most companies of non-trivial size is designed to expose you and obfuscate the company. Interviewers get 50 minutes to grill you in front of a board. You get 5 minutes at the end, when all you really want is a pee break. Interviewers want you to describe past experiences and projects and incidents in utmost detail. In turn, they expect you to understand that discretion prevents them from sharing many specifics about

yes, the issue is when you are asking these questions in interviews for jobs where you don't need them.

Employers generally refuse to openly discuss it with anyone who isn’t a retention risk, which made interviews unattended very weird when I would give perfectly honest answers to the candidate about “why is this position open?” (a question that most candidates don’t ask because they’re desperate for employment).

Ideally yes, one would ask these questions. Practically, there is not enough time. You'd be lucky to get even 5 minutes to ask all these questions. Even if you have the time, you have to ask these questions in a diplomatic manner. Unless you are a well known hot shot in your field, a job interview is marred by power imbalance and any signal that you are cynical, confrontational, question authority etc. will count against you. So do ask these questions, but be careful how you frame them.

Despite what many people will tell you this isn't the time to ask some carefully crafted question which will make you appear to be a better candidate. Sure, there are interviewers who believe this, but anyone who thinks that way is not someone I really want to work with anyways.Instead, this is your opportunity to fill in any blanks you might have regarding if you actually want to grace them with your presence. IMO "no" is a perfectly valid response to that question as it is

As an interviewer or hiring manager why wouldn't you ask about it?

That's a bit much - it's rare that a company doesn't have something broken about its hiring process, even good/great companies. If you want to work there otherwise, what does it hurt to learn the expected answer for fluff questions and recite it when asked?

Interviewers directly asking whatever bothers them is fine IMHO. The alternative is keeping a negative impression when there could have been an insightful exchange, and the candidate also gets to know what to expect from the company.

Yes that's a good question, I wouldn't like to have that without notice in an interview :)