Here goes another brain talking about this theory vs law issue.
"Put succinctly, a theory is a Law that hasn't been around long enough or doesn't yet have enough data to become a Law."
Dr. Michael E. Maguire
Department of Pharmacology
School of Medicine
Case Western Reserve University
Gravity exist because the law of gravity is something that we all should agreed on that there is such a thing as gravity.
However, the theory of gravity described the law of gravity and we have seen that theories have been debunked from time to time, in due time thus why scientists are smart enough to make it a theory so that others in the distance future can find something better with such theory to either debunk it or make it better.