Of course it's difficult. Even if you could convert it to cash you wouldn't be able to deposit in any bank or meaningfully use it. The moment you do anything with it you'll trigger anti money laundering laws and have to explain where the money came from.
From a criminal perspective you may not have to launder it. Just deposit your XMR/ZEC into an exchange and sell it. If they ask, say you bought it years ago at $10.
