My accent isn't quite what it should be. There are elements of Liverpudlian in there, even though I've only been there twice and was just passing through on the way to the Isle of Man. By rights I should have a Yorkshire accent, diluted with RP (from the grammar school) and with a smattering of Midlands. I'm sure the scouse element comes from my childhood preoccupation with Merseybeat bands. I've been told I sound like John Peel the radio DJ (RIP).....I used to listen to his shows a lot. He was Liverpudlian too.
I don't know why. I think one-A-N may be right about it being down to spending more time listening to my heroes than my peers. Also like Pensieve I often find it easy (and fun) to mimic accents, though I can't do 'em all. I picked up a temporary Westcountry accent while on holiday in Cornwall as a child, which I used to great effect when I acted in the youth club pantomine........I think I did that because I was very self-conscious about my mumbly "normal" voice, and noticed that I could project my voice better when using an accent. And it got me my first girlfriend, because my performance charmed her. I'm pretty sure that my usual voice wouldn't have impressed her at all.
To this day, when I'm working up a new song, I'll try to mimic either a real singer who I admire, or a vocal style that's used by singers typical of the song's genre. I remember trying a cockney accent on "Lazy Sunday" back in 1969, and I was amazed at how much better it sounded on the recording than everything else I was doing at the time. I never really sing anything in my "own" voice, though the shortfalls in my ability to copy a voice perfectly make my voice recognisable as me.