Why do British people never sound British when they sing?

well I saw a documentary about the early days of pink Floyd that said something interesting regarding this question. they said during the "British invasion" all the British bands were trying to sound American (like the rolling stones) and finding inspiration in American black culture like blues and jazz but one exception in this was Sid Barret, first singer of pink Floyd, who actually sounded British when he sang and this was one of the things that made him stand out.