Here's why:

* Myosin is a motor protein that plays a crucial role in muscle contraction and other cellular movements.

* Thick filaments are primarily found in muscle cells (muscle fibers), where they interact with thin filaments (made of actin) to generate force and movement.

* The structure of a myosin molecule resembles a golf club, with a head region that binds to actin and a tail region that interacts with other myosin molecules to form the thick filament.

While myosin is the primary protein in thick filaments, some other proteins are also present, including:

* Myosin binding protein C (MyBP-C): This protein helps regulate the interaction between myosin and actin.

* Titin: A giant protein that acts as a molecular spring, providing elasticity to the muscle fiber.

Therefore, although myosin is the most prominent component, a few other proteins contribute to the structure and function of thick filaments.