What is the reason behind bots spamming marginalia? What’s the motivation? What do they gain? I always wonder about these things.
Many of these bots are exceptionally simple - zero tailoring, just scriptkiddie copy/past/run stuff.
They could simply iterate through a list of websites inputted by the user. Said list could be some curated list you find on blackhat forums, which is just a collection of websites with traffic over a certain threshold. Doesn't say anything about the content or what type of website, just the URL.
Then it does a simple operation to map the website - as well as checking for input forms. If an input form is detected, it does a POST operation. If there's an error, timeout, or whatever, it simply moves to the next one.
This of course sucks if you try to run a search engine - because even the simplest of bots will succeed when your website is literally just one website, with the text/input field right there in the front, and with no captcha or similar to dissuade legit users.