Question

Why is gravitational force always attractive, why not repulsive ?

Answer 1

It's simply what we also observe in nature. This fact is also reflected in the Newtonian formulation of gravity where the force is
\[ F = - \frac{Gm_1m_2}{r^2} r_{vector \ direction \ from \ mass1 \ to \ mass 2 } \]
As the masses of the two objects \( m_1 \) and \( m_2 \) are both positive, the force \( F \) is always negative which means the force is always attractive.