New idea in Sicilian for white?
On e4 the White pawn is strong, controlling the important central square d5 (which Black has given up some control over by playing c5). You might think that it is just as good to control d6, but d6 is less central.

The loss of time is also significant. You spend a move to put the pawn on e5, and then another move to defend it with the queen. You will have to move the queen again, or your g-pawn, to develop your king's bishop. That makes three moves you could have been spending developing minor pieces or central pawns or castling! Half a pawn seems a fair evaluation of that loss of time.

Finally, the pawn may be vulnerable on e5. Black has a pleasant choice whether to play g6 and Bg7, or e6, Ne7 and g6, or f6 exchanging the pawn but getting fast development. White will have trouble bringing more pieces to the defence of e5: in particular it won't be easy to support it with a pawn as Black controls d4 and White's knight blocks the f-pawn.