In this puzzle, why does white play dxe5? I came across the following puzzle on lichess (black to play):

[Event ""]
[Site ""]
[Date "????.??.??"]
[Round ""]
[White ""]
[Black ""]
[Result "*"]
[FEN "1k5r/1pp2q2/p2p2n1/4pp2/2PPP1p1/1P2B1P1/P2Q1P2/2KR4 b - - 0 1"]

1...f4 2.dxe5 
    ( 2.Bxf4 exf4 )
2...fxe3 3.Qxe3 dxe5 *


Which apparently proceeds as follows:


... f4
dxe5 fxe3


f4 is clearly a good move, since both sides have triple protection on the f4 square so black always ends a piece up. What is confusing me, however, is the following move by white – dxe5. This is odd, since fex3 is a queen threat, and hence a forcing move. Stockfish, on the other hand, agrees with dxe5.

Why can white not play Bxf4, simply taking the pawn and also avoiding the queen threat?
It is quite pointless analyzing moves in lost positions. 

Here in either line white will lose a bishop for a pawn. 

A queen threat is just that, a threat. Why are you so much afraid of it? The game could continue


... f4
dxe5 fxe3
Qxe3 Nxe5


In the other line you'd have


... f4
Bxf4 exf4


Both are very lost positions.

Why the computer picks the first over the second line, who knows (who cares)? Perhaps it prefers it because the white pieces get slightly more space.

In a practical game, other than resigning, my first choice would also be dxe5 for two reasons:


gives black the chance to blunder with dxe5 after which white can mate starting with Qd8+
it opens the position which gives more chance for swindles for the lost player.