In the bad old days, when I worked for a living, I never gave anyone a maximum score in appraisals - even someone who was excellent in every way 'only' got, e.g. 4/5 or 'very good' rather than 'excellent'.

My boss for seventeen years, a man I held in very high regard, always said that you should never give full marks, no matter how good someone is because, by giving the top mark, you remove the employee's motivation to try even harder, and that everyone, no matter how good they might be at their job, is capable of doing 'better'.

Makes sense to me - obviously! 👍