If you owned a restaurant called Fred's Diner, you might have a website called freds-diner.com. If a delivery company gets the domain freds-diner-restaurant.co

If you owned a restaurant called Fred's Diner, you might have a website called freds-diner.com. If a delivery company gets the domain freds-diner-restaurant.com, then they're competing for your traffic. And their domain might end up higher in Google search results, leading customers to order there. So I don't think it's necessarily the case that they're getting customers they otherwise wouldn't have. Customers that are only willing to order from Uber Eats etc. aren't going to look for the restaurant's website anyway, they'll just go through the delivery company's website.