I dont know what kinda answer your looking for apart from the obvious.
Their voices are manipulated in the studio to sound perfect, while live they have to rely on vocal talent. Which unfortunately some people just dont have.
Because they edit their vocals in the studio and they are usually moving around while performing on stage. I will say that most pop stars aren't terrible in concert.
Because it's way easier to sing in the studio? They can sing a lyric multiple times until it comes out perfect unlike when they sing live.
And at the ones saying "no talent" at least say no vocal talent because writing every song, playing multiple instruments and captivating the gp (something atrl's "super talented" indie girls can't do and that results in some atrlers complaining about how there's so much wasted talent in artists that aren't successful) are also talents.
but the live version 
at the ones saying "no talent" at least say no vocal talent because writing every song, playing multiple instruments and captivating the gp (something atrl's "super talented" indie girls can't do and that results in some atrlers complaining about how there's so much wasted talent in artists that aren't successful) are also talents.