So that a winning gain would be the 'opposite' of a loss, they are balanced. Your situation is enhanced by some factor if you win, and diminished by the same factor if you lose.
Of course the actual amounts, percentages, proportions look bigger for the win compared to the loss, but that's just maths.
Your stake should grow or shrink by the same factor if you win or lose.
If you win, your stake is multiplied by 1.5.
If you lose, it should then be divided by 1.5 (multiplied by 0.66..).
But is in fact multiplied by only 0.6.