I finally got to experience this from the inside. I was on the team that interviewed people to back fill my position after I was promoted.
We didn't interview 1 external candidate. Promoted someone from below and then hired a new entry level person.
We realized our internal hire has less experience, but they were the safe fast option that could get started right away.
It's so, so frustrating that so many places require a job to be posted even when there's an internal candidate and it's already been decided. I work in government where we're often hard-required to post all jobs and it sucks to see so many people applying for a job when I know they absolutely will not be considered for the role.
In my experience, a majority of job postings are essentially fake because it's already been decided, and I hate it.