I bought a ticket through justfly.com, but I might need to cancel it now. I was informed that the ticket is nonrefundable, which is fine--I expected this. I was also told that there would be an additional cancellation fee. This seems strange to me. Is there any reason that I couldn't just not cancel the ticket to avoid the fee, and then simply not show up for my flight?
Non-refundable does not mean non-changeable. If there is a cancellation fee or a change fee stated for the ticket, that usually means you have a changeable ticket.
In your case canceling the booking should result in the airfare you paid minus the cancellation fee becoming a credit that you can use for a future ticket on that airline (often with a time limit for use).
I don't think justfly.com can charge an additional fee on top of the airfare you paid.