1- Companies understanding that a good user-interface is a must for their product. HN crowd are known for being anti-JavaScript, but modern web-apps are incredibly powerful and useful. This means you can't make your back-end developer glue together a JSP and call it a day anymore. So front-end overall is in high demand.
2- React helped standardize the way we do front-end. Yes Svelt, Vue and Solid are all great. But the ecosystem and the ability to hire from a large pool of talent without needing to train developers on your niche stack is a huge benefit.
3- React is easy to start, hard to master. When interviewing you'll likely be seeing a 10:1 ratio of boot-camp grads vs developers who have dealt with complex React apps at scale. This means an experienced React developer can ask for a higher salary.