Nostr data is stored in the relays. If a relay is public, its data can be scrapped by anyone. If the relay has restrictions, data won't be publicly available. Paid relays are just one way of restrict access to data/resources. Also, could be relays allowing access to data not just for a payment, but using a trusted keys configuration. A relay allowing scrapping on demand by a fee is the way how we can finally sell our own data