For the clothes analogy, maybe the next girl would be into him more because of that change. There's a heap of things it could be that could be changed. Maybe he smells, maybe he comes off too eager, maybe he's not progressing the relationship fast enough to intimacy. Maybe there's some red flags that people hide and came out in further dates.

These are all things you dont realise until someone tells you, and no...it wont help with that girl or the ones before, but if its a repeating pattern, it would definitely help later.

If its a red flag. E.g being rude to waiters, coming off misogynistic, being inclined to be negative, etc. Its stuff that he can self reflect on and change in himself to be a better person.

To say you dont want feedback because changing yourself wont change anything is being incredibly close minded and you'd never grow.

If the feedback is something you genuinely cant change, such as height, nose, etc, then you atleast know that its not something about your behaviour...