I think it's more an issue of culture than talent. As I understand it, you'd find far fewer people in South Africa, for example, who said they couldn't sing than you would in Britain.
For most people in Britain, music is a consumer product, not a participatory activity. It has reached the stage where singing is viewed as almost embarrassing, unless it's performed by "artists" who are singing from behind a microphone or on recorded formats, or at karaoke evenings where the audience can take delight in how badly the singer is performing. How often have you heard someone tell you that they sing in their car (when alone!) or in the shower? The desire is probably there, but there is a cultural resistance to it.