That’s the big change that naturalism (nature is all there is and you did not evolve to understand it correctly) has created in science. Evidence isn’t critical any more.
From Natalie Wolchover at Quanta:
String theory (or, more technically, M-theory) is often described as the leading candidate for the theory of everything in our universe. But there’s no empirical evidence for it, or for any alternative ideas about how gravity might unify with the rest of the fundamental forces. Why, then, is string/M-theory given the edge over the others?
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This basic sequence of events has led most experts to consider M-theory the leading TOE candidate, even as its exact definition in a universe like ours remains unknown. Whether the theory is correct is an altogether separate question. The strings it posits — as well as extra, curled-up spatial dimensions that these strings supposedly wiggle around in — are 10 million billion times smaller than experiments like the Large Hadron Collider can resolve. And some macroscopic signatures of the theory that might have been seen, such as cosmic strings and supersymmetry, have not shown up. More.
See also: Post-modern physics: String theory gets over the need for evidence
and
Question for multiverse theorists: To what can science appeal, if not evidence?