Why Qe1 in the KIA? Why not Re1? rnbqkbnr/pppppppp/8/8/8/3P1NP1/PPPNPPBP/R1B1QRK1 w kq - 0 1


I see that many players play Qe1, but why not just Re1? What is the difference? Doesn't the queen on e1 also make the potential weakness of a black battery from c8-h3 by exchanging the light squared bishops?
One reason the set-up with Re1 is less popular could be that it loses a pawn in a certain quite common variation:

[FEN ""]
[Title "KIA with Re1"]
[Startply "15"]

1. Nf3 d5 2. g3 c6 3. Bg2 Nf6 4. O-O Bf5 5. d3 h6 6. Nbd2 e6 7. Re1 Be7 8. e4?


Do you see black's tactic?


   After 8. ... dxe4 9. dxe4 Nxe4 10. Nxe4, white has opened the file allowing for Qxd1!, forcing the Rook to abandon the Knight and black ends the exchange sequence up a pawn.