Question to native English speakers & music listeners

Thank you, kirkk, to give such detailed reasonable answer.
Last paragraph makes sense but, I shall tell I did say "mainly", i.e. generally, not every single British artist sings as American. Indeed, people can detect that Davy's British English.
Still, many British singers write songs & in studio albums sing lyrics with American accent. It's songs *they'd* written, nobody to impersonate, yet they sing with such phonetic patterns as "t" saying as "r", round vowels they say as "a", like "not" as "nut", "jolly" as "jully", "orange" as "ahringe", "new" as "noo" etc.
For example Welsh singer Shakin' Stevens, Oasis with ease delete their really-difficult-to-decipher-in-interviews Manchester accent, instead sing like Americans. Bonnie Tyler sings like Texan citizen.
It's really interesting to hear they switch to it.
Anybody got anything to add to this what looks like interesting subject to discuss?
Thanks again, kirkk, to kickstart it by giving your 2 dollars to the thread.

^ Interesting points, thank you g00v.

Theory about *country* artists being sonically American adds dimension to discussion. New avenue, if you will. Didn't think it.

Ditto rhymes "Californ-i-a", albeit IIRC nobody says it like that, i.e. it ain't "accent switch" case but band's invention, creative liberty.
Interesting point still.

Re: Oasis, if you listen to Liam's & Noel's interviews, especially Liam's, he speaks in jolly thick native accent, it isn't neutral English, reaaaaally difficult to get what he speaks about. But in songs he sings crystal-clearly, you can tell what he sings. Maybe accent is still intact but to these ears, he sings lyrics like American singer will. I don't detect it as easy as you. But when I mentioned Oasis, initial instance been Noel, actually. "Don't Look Back In Anger" - really identical to how American singer would sing it, would Oasis be U.S. band.

What maybe - even likely - puzzles is that British singers, including Scottish mentioned by you, say/ sing words in American way - see previous reply I'd written - especially when they say "but" as "bar" & any t --> r change.

Even somebody who hates by her admission pop music with fashionable accent adaptions & stylings, loyal to her Welsh roots & traditional Welsh folk/ celtic music, even Mary Hopkin used American accent in Eurovision song "Knock Knock Who's There" - "but instead" --> "bar instead". She didn't sing the title "Knuck knuck" but she did get few Americanizations. When she could sing it like British thru & thru.

...or is t-to-r very common in U.K. too? Is it not just American way to speak? But I didn't hear in any British film seen.
Paging British English speakers.

Btw, it isn't big surprise that various British citizens - Scottish, Welsh, Irish - when they sing would lose their local accents & sing easy-to-decipher neutral English. What's really interesting is they singing in American accent, meaning strictly the original material, covers discount. 2 people brought to discussion why it could be, thanks to both posters.

I read few years back about it incidentally & somebody in the Internet stated that maybe everybody sings with American accent due to its ubiquitousness & said it's cliched, singable accent, catchy, stereotypical. Something to the effect. Hm, not really sure.

Anyhoo, anybody else to add *their* theories, without repeating kirkk & g00dvibrations? New replies welcomed.