A question about English accents?

Obviously, the British English accent evolved first – and though there are several distinct accents throughout GB – there is a certain British accent that is different from the American.

The American accent, of which there are also several, is distinct and distinguished from its British counterpart, and ancestry.

But correct me if I’m wrong, except for a few British singers with very distinct, heavy – perhaps Manchesterian accents, many of them sound American when singing.

Why is that?