It could be too warm. They need a 2 - 3 month period of cold and dark to make roots before being brought into warmth and light. I put mine in an unheated shed in the garden. They need to be down at 9 or lower. Does it have any roots?

No roots at all and it's a bit soft, I guess it's mostly rotted, right?

All other bulbs are alive and healthy, I have 2 kinds of narcissus in 4 bulbs, a daffodil, and an iris, planted in the same conditions and all of them have produced beautiful leaves, except the hyacinth :(

Could it be spoilt from the beginning?