whether or not string theory is at this point grifty and weird, the theoretical basis for it is far stronger than you would think based only on reading critics / pop sci explainers. It is not like, missing any obvious physical facts in its foundation. Rather it is trying to say: look, we have this zoo of particles with seemingly random masses and properties; is there same lower-level framework which can produce the zoo that we see according to a simpler list of rules? The obvious choice for this, especially given some of the "hierarchies" of particles that are observed, is that they are in some way resonant modes of some kind of underlying object. Which is where you get the strings from. (Which might sound like a weird justification if you are not aware of all the other aspects of physics which get explained as resonances of fields; this is a standard sort of justification which there's a lot of good reasons to be interested in, at least initially.)