Proofs of theories are limited to the self-contained systems of analytical logic and mathematics, while science explains nature as a dynamic whole. Proofs are final and binary - two features that cannot exist in something as living and changing as science. Also, theories can be falsified when new evidence is discovered.
A theory is accepted by scientists when it exists as the best explanation among other alternatives, if there are any at all. The acceptance of a theory depends on the emergence of a better one or on its falsification by new evidence. Even scientific fact, which is defined by The Free Dictionary as a confirmed observation accepted as truth, is not final.
The aim of science is to explain nature and to eliminate rival theories. Some scientific theories are more widely accepted because they are either the best explanations of a phenomenon or simply more credible. However, credibility is not a true scientific criterion.
Even if a theory is falsified, that does not necessarily mean the phenomenon it pertains to is also called into question. For example, the theory of gravity is an explanation of how gravity works, but if it were found to be flawed, that would not mean gravity does not exist at all.