Because, you're obviously really shooting eyebeams through the scope.

But seriously, have you ever had a no-scope war in Counter-Strike Source? It's hard.

probably because firing a sniper rife from the hip accurately is pretty hard to do

just a guess

^^^

I like hating on MW2 for its failness.

You can fire an M82 from the hip, but expect your shoulder to at least get dislocated.