The trouble is one of putting the cart before the horse.
Nature is presented to us as geometry ... not mathematics. Normally, one supposes a geometrical solution to a physical problem THEN mathematics is fitted to it (to see if it might be disqualified because of quantitive contradictions to observation).
Not so with string theory. Here, geometrical models are fitted to mathematical relationships in the hope of finding a good fit. That is, fitted to what string theorists have available for a "fitting".
The main problem in particle physics is that there are numerous particles created in experiments but they are not in any discernable order (none that anyone can presently find). If they were evenly spaced in mass ... one next to the other and increased by some fixed amount ... the job of physics would already be over.
There is an expectation that good order ought to be found. And that the closer one gets to the "ultimate", the more readily discernable that order should be ... but it is not. Hence, despair. Hence, mathematical "mysticism", i.e. roll 'dem bones 'n read 'em.
Having a mathematical relationship in hand is worthless without the geometry which it describes and that geometry must first be derived from other logical-geometrical models which are known to be true and mutually consistent. A mathematical equation can mean any number of things depending on what it is applied to. Picking something out of the air which seems to fit is more mystical than realistic.
Mathematics is the description of geometry. Geometry is the thing itself.
Nature is not presented to us as mathematics. It is presented as geometry. That is the only true, logical concrete given to us. Our job is to identify and describe it ... not to invent it.
In their defense, string theory could end up as a real model of existence or part of it ... somewhere along the line ... but a lot of people are using up their careers on a thing which, if proven true, could not even be transmitted to the general public in any sensible way.
String theory solves (hopes to solve) the particle zoo by vibrating strings [in ten dimensions at the Planck scales mind you]. Since the vibrations are stable as standing waves only ... these would ostensibly represent the observed particles. They might then break, conjoin, and thus otherwise create others dissimilar to themselves ... and ... the plethora is thence displayed explicit. Beauty abounds!