Why does it harm credit score? Although I believe it's the case, I don't think it should be as it disincentivises competition.
Constantly opening and closing bank accounts and having multiple hard searches in a short space of time. That's if you do loads in one go like I just did. But meh. Score won't be impacted that much I doubt. I will update in a few months. It usually recovers after 12 months so I am told.