While it’s true that chatbots fetch information from websites in response to requests, the load from those requests is tiny compared to the volume of requests indexing content to build training corpuses.

The reason is that user requests are similar to other web traffic because they reflect user interest. So those requests will mostly hit content that is already popular, and therefore well-cached.

Corpus-building crawlers do not reflect current user interest and try to hit every URL available. As a result these hit URLs that are mostly uncached. That is a much heavier load.