How do you know they are “unused”? The web and e-mail are just some services on the internet, there are many others, you can invent your own. These services could be on subdomains or hosts that are only known to those who need to know. In other words, the use of domains could be private within a group. Even if this sounds unrealistic, it’s an alibi the squatters could use to escape forced expiration. Only if the Domain has no functioning authorative name servers, could you claim the domain is truly “unused”.