You're absolutely right. Unfortunately the broken-ness of the interview process is not limited to the interview itself.
I've interviewed around 40-50 folks for $role at $wildly_successful_megacorp.
My qualifications: zero training, zero oversight.
I'm getting a lot better and more consistent. But I have still left a lot of interviews thinking how poorly I have done, and needing to reflect on how things could have gone differently.
It's very easy to think of interviewing folks as a chore or merely a favor to $other_manager. For something so vital to the long term health of the company, it's really appalling how little effort is put into it.