Why after my stroke my hand remains curled in thevfetal position?

Damage: Could've damage to the part of the brain which controls your hand. Your neurologist can give detailed explanation.

Loss of brain cells: By definition a stroke is a loss of brain tissue which leads to loss of function of the body in the distribution of the body that brain tissue controls. While improvements in function can occur with healing of areas of the brain and due to brain plasticity, brain tissue does not replace itself. The curling of the hand is due to loss of muscle strength from the brain loss and increased tone.

Secondary rxtn: When upper motor neurons in brain are damaged the body is programmed to act defensively, and in absence of balanced muscular position, the elbow and wrist get flexed and the hand curls up, work with a hand therapist and ot, as gradually this will loosen up.