I suppose that they just keep referring to the website in their chats, and probably they have selected the search function, so before every reply, the crawler hits the website

The site is about a particular type of pipeline cleaning (think water/oil pipelines). I am certain that nobody was asking about this particular site or even the industry its in 15,000 times a minute 24 hours a day.

It's much more likely that their crawler is just garbage and got stuck into some kind of loop requesting my domain.