Bandwidth isn't free, not at the volume these crawlers scrape at; serving them random data (for example by leading them down an endless tarpit of links that no human would end up visiting) would still incur bandwidth fees.

Also it's not identifiable AI bot traffic that's detected (they mask themselves as regular browsers and hop between domestic IP addresses when blocked), it's just really obviously AI scraper traffic in aggregate: other mass crawlers have no benefit from bringing down their host sites, except for AI.

A search engine has nothing if it brings down the site they're scraping (and has everything to gain from identifying itself as a search engine to try and get favorable request speeds - the only thing they'd need to check is if the site in question isn't serving different data, but that's much cheaper), same with an archive scraper and those two are pretty much the main examples I can think of for most scraping traffic.