Tailwind UI is tool companies buy to save dev time mostly on internal/back office tools. It's usually bought per project. The math is pretty easy - if it saves you few hours of devtime you buy TailwindUI. Shadcn and bazillion other similar things are certainly competition but TailwindUI is very broad and of high quality so why not pick the nicest version.

The problem is that Tailwind is extremely portable (thats why it's so popular) and since LLMs have been fed all TailwindUI code... people using LLMs don't even have to know that TailwindUI exists they just get some Tailwind styled components. They would probably look pretty confused if you told them you used to buy these templates.