It's important to avoid conflating string theorists with all theoretical physicists. Plenty of people in particle physics either don't believe in string theory or don't think it can make useful predictions any time soon, even if it were assumed true. Furthermore, the vast majority of people called "string theorists" don't even work on traditional string theory day to day, but on more concrete ideas that have been par…
It should really be called String Hypothesis. Theories in science are generally for something that's near 100% proven.
A hypothesis is ideally 'atomic': it's making a single assertion that should be falsifiable by experiment.
A theory provides a specific way of modeling the elements of some field of study, and how those elements interact with one another.
It should be structured in such a way that it can describe the components of any experiment that might be set up to confirm/reject a hypothesis in this field.
And once an experiment is described in the terms of some theory, the theory should provide a systematic way of calculating what the result of the experiment should be.
That's where the connection between hypotheses and theory comes in: actually conducting experiments assigns either Acceptance or Rejection to a set of hypothesis; ideally, the theory assigns the same Accept/Reject values to the same hypotheses in its predictions (this is probably never 100% the case in practice though—esp. not in an active field of study).
The structure of String Theory is much closer to theory than hypothesis. (It may have limitations in how much it models physical 'experiments,' but it's at least much more of a 'system description' than an atomic assertion.)