Locked iphones are easy to resell for their parts but you get pennies on the dollars. Last time I checked (long time ago), you could get the latest gen top tier model in perfect condition on ebay for less than 100$ with a blacklisted IMEI (they work but can't use cell network). For a fully locked phone, I doubt the thief would get more than 10% of the original value. They might not throw it in the trash, but they also won't go out of their way to try to steal the one you have in your pocket.