Competitors use them to ever so slightly undercut your prices, get a higher position on said comparison sites, and run you out of business.
If you aren’t on comparison sites at all because of your anti-scraping measures, is that better?
Not to defend the practice but I think the intent is to allow scraping (or API access) only by the price comparison site but not by competitors. (Why wouldn't the competitors then just scrape the price comparison site? Because that site also has anti-scraping measures in place...)