What we've observed is that this file is never requested by any LLMs. At most, it was requested by bots from BuiltWith and WebPageTest, but not by major LLMs.
Can you check your logs to see if llms.txt is being autonomously read by any popular LLMs?
(1) https://llmstxt.org/ (2) https://github.com/tirrenotechnologies/tirreno