I think it comes down to how incentives are structured. In my experience, if someone who is promoted from L to L+1 fails to succeed at that new level, that pers

I think it comes down to how incentives are structured. In my experience, if someone who is promoted from L to L+1 fails to succeed at that new level, that person's manager is dinged for pushing a promotion that the person wasn't ready for. Conversely, an external hire who comes in at L+1 and fails to succeed is chalked up to the difficulties of hiring, with no negative consequences for the hiring panelists. As a result promotions are much more conservative than hiring. Which definitely sucks.