>>12774257because it is basically a solved problem. if you think about it, everyone studies classical strings in undergrad or grad physics. Fetter and Walecka, a common grad textbook, explains classical strings in depth. D’Alambert did the important steps in like the 1800s. and what makes it weird, as a classical system, is that even though it is nonlinear, nonetheless it is exactly solvable.
so the challenge of “string theory” i.e. modern quantum (relativistic) string theory is to simply quantize the known classical physics and then to study any anomalies or weird quantum effects in a well-understood classical system. even in the early 70s they realized that quantizing it destroys the theory unless it lives in 26 dimensions. so it went into a wacky status. super symmetry was needed to make strings behave like fermions, so you get another level of wacky ness, but at least that reduces the dimensions to 10 instead of 26. so they solved that, and finally the challenge was to take care of quantum “anomalies” which, in normal quantum field theory, are a big challenge (a prototypical example is the chiral anomaly in electroweak theory).
but in 1984 the anomalies of string theory were understood and the theory was shown to be free of any anomaly-related problems. so you had an exactly solvable classical theory, and it’s quantization was proved to be doable and sensible. so it was basically done at that point.
that’s why nobody works on it any more. it’s solved. the main push since then was to tie up loose ends and then get into model building. and model building is a different game in string theories—it is highly constrained so you can’t easily just fit it to data—instead you need to work out a full solution and check if it reproduces what you want. so you have a theory that is known, finite, and solved, but fitting it to data is nearly impossible. that’s why nobody works on if
