This may come as a shock, but some engineers don’t want to be promoted. They’re happy being an engineer. They want to focus on code and building, not on leading, or mentoring, or helping define process.
I’m speaking from experience. As an engineering manager, I’ve been surprised many times by engineers bluntly stating they “are happy with their current role”. Some proactively. Some during career growth discussions. I was impressed every single time. There was an undeniable clarity.