1. I think there are two reasons why string theory is cool (other people may have different opinions). Please note that none of these two reasons are directly related to the extension of Standard Model. 1.1. String theory is the only theory so far that can mix gravity and quantum mechanics, and it can be even used to derive Hawking entropy of a black hole from "first principles" (see paper by Strominger and Vafa). The obvious trouble is that the black hole in question lives in five-dimensional space and is unrelated to the real-world black holes, but this is way better than what one can get from Standard Model physics (which is, no gravitons for you).
1.2. Through AdS/CFT correspondence, string theory can be used to describe quantum field theories that are not related to string theory by themselves. This gives a very strong tool to study these quantum field theories, and the paper by Maldacena that discovered this correspondence is one of the most important papers in the field.
2. It is true string theory is unusable as of now to derive the Standard Model physics (and provide extensions for it). Unfortunately, I would say that hardly any papers in high energy _theoretical_ physics currently address Standard Model physics. Roughly speaking, in late 1970s, after quantum chromodynamics was established and the asymptotic freedom was discovered, it turned out that it is extremely hard to compute many things we are generally interested in. At this point, high energy theoretical physics split in two sub-areas: phenomenology (which tries to extend the Standard Model to derive things like neutrino mass) and theory (which is a more formal theory and tries to answer questions like "how to quantize gravity"). One can argue that this makes hep-th an area of mathematics, and I would agree with that (eg in Cambridge theoretical physicists are in the same department with applied mathematicians).
2.1. The things theoretical physicists study tend to pop up in various places, even if the original motivation is misplaced. Even the string theory itself originated as a way to explain the Regge trajectories (which were explained with quantum chromodynaics afterwards), and not to quantize gravity. For a more practical example, Witten introduced topological quantum field theories long before anyone understood how to apply them to real-world physics.
3. I do not agree that string theory dominates the hep-th field. I would say that its popularity changes with the time, going up and down. While the main conference in the hep-th field is called "Strings", the talks at it are not necessarily related to strings theory, and at the 2025 conference I'd say that only 1/3 of the talks were anyhow related to the strings theory. Moreover, there is no hard division between people working on string theory and people working on other hep-th subjects, so that e.g. Witten made many contributions to hep-th which are not anyhow related to string theory.
3.1. As for the push to do string theory that eg Sabine Hossenfelder alludes to, I'd say that I experienced no such push during my MSc and PhD studies. I've written four papers, and worked on a couple of projects that did not become a paper, and out of those, only one was dedicated to string theory.
3.2. On the other hand, the more fringe theories that can provide alternative to string theory are also more high-risk endeavors (as you are quite likely to fail to produce anything coherent within a typical timeframe you allot to write a paper). Hep-th is strongly underfunded, and I believe, that with greater funding (and less need to publish-or-perish) some people would also pursue the more fringe directions in hep-th.
3.3. A comment on the naming: hep-th is a field which is very hard to name. The name I use is the traditional one (and is used as eg a name for the field on arXiv). However, many things derived by the physicists in the field are not anyhow related to the high energy in the literal meaning of the words "high energy". When talking to people at a party, I say that I studied string theory, because the name is catchy and it rings a bell, but this way of referring to the field is definitely a misnomer.