Gravity is considered a theory because "theory" in the scientific context has a specific meaning. In science, a theory is a well-substantiated explanation that encompasses a broad range of observations and is supported by a substantial body of evidence. It goes beyond mere speculation or guesswork.
Gravity, as described by the theory of general relativity, is a fundamental force that governs the behavior of matter and spacetime. It explains how massive objects, such as planets, stars, and galaxies, influence the curvature of spacetime and how other objects move within that curved spacetime.
Despite the overwhelming evidence supporting the theory of general relativity and its successful predictions in numerous experiments and observations, including the bending of light around massive objects and the accurate calculation of the precession of Mercury's orbit, scientists continue to refine and test the theory. This ongoing scientific process involves further investigations, experiments, and observations to confirm, modify, or expand our understanding of gravity and its interactions with matter and the universe.
Scientific theories are subject to revision and refinement as new data and observations emerge. This is an essential aspect of the scientific method, as it allows for continuous improvement and deeper understanding of the natural world. Therefore, even though gravity is an observable phenomenon, the theory of gravity itself is continually evolving and subject to further investigation and refinement.