As companies grow, they tend to move away from subjective performance reviews like that and toward more objective metrics. Otherwise, it's too easy for personal politics to contaminate the promotion process. Employees are incentivized to find whichever manager will give them 5 star reviews no matter what, and managers are incentivized to be that guy, because then they have access to the best employees. When a company is small, and everyone knows everyone, this is not an issue. But when 90% of the company is a stranger to you, you need more objective metrics to rely on.