That's because it is stupid. Very, very stupid.
Consider this game: https://www.chess.com/automate/1465389
Here, white moves 15. Re3.
That move is clearly bad, as 15...Bh6 wins black the exchange.
Checking 15. Re3 with engines:
Stockfish.js 12 depth=14: loses 89 centipawns
Stockfish.js 12 depth=16: loses 146 centipawns
Stockfish.js 12 depth=18: loses 64 centipawns
Stockfish.js 12 depth=20: loses 92 centipawns
Komodo.js 13.2 depth=14: loses 77 centipawns
Komodo.js 13.2 depth=16: loses 73 centipawns
Komodo.js 13.2 depths=18: loses 39 centipawns
Komodo.js 13.2 depth=20: loses 60 centipawns
Literally everything says it is an inferior move.
---
Another example: https://www.chess.com/automate/1455195
White loses a completely drawn endgame with 86. Bf3
Black responds 86...Bxf3 and uses the extra pawn to win the game.
Literally everything says it is an inferior move.
tl;dr Automate uses a turd to calculate moves.
Is it possible that the computer is using the values detailed in the setup? (7 for queen; 4 for a rook) That would change the results of calculations on moves like the one you posted. The exchange sac becomes more like a pawn sac.
Endgames are very difficult for computers. A depth of 18 is not sufficient for such as the one you posted.
That's because it is stupid. Very, very stupid.
Consider this game: https://www.chess.com/automate/1465389
Here, white moves 15. Re3.
That move is clearly bad, as 15...Bh6 wins black the exchange.
Checking 15. Re3 with engines:
Stockfish.js 12 depth=14: loses 89 centipawns
Stockfish.js 12 depth=16: loses 146 centipawns
Stockfish.js 12 depth=18: loses 64 centipawns
Stockfish.js 12 depth=20: loses 92 centipawns
Komodo.js 13.2 depth=14: loses 77 centipawns
Komodo.js 13.2 depth=16: loses 73 centipawns
Komodo.js 13.2 depths=18: loses 39 centipawns
Komodo.js 13.2 depth=20: loses 60 centipawns
Literally everything says it is an inferior move.
---
Another example: https://www.chess.com/automate/1455195
White loses a completely drawn endgame with 86. Bf3
Black responds 86...Bxf3 and uses the extra pawn to win the game.
Literally everything says it is an inferior move.
tl;dr Automate uses a turd to calculate moves.