Rigor mortis occurs after death primarily because:

medium

AToo much ATP forces myosin to stay attached to actin

There is no ATP to detach myosin from actin, so cross-bridges remain locked

CAcetylcholine is broken down too quickly

DActin filaments are destroyed, preventing overlap

EThe sarcomeres permanently lengthen due to excess Ca2+ pumping

Explanation

ATP is required for myosin to detach from actin. After death, ATP production stops; cross-bridges lock, producing stiffness until proteins degrade.

Source: entermedschool.org