Imagine the conversation they had 2 years ago when they registered their .net domain.
Maybe 2 years ago, they were deciding on their corporate identity: maybe ABC, DEF, or GHI, ...
They decided on ABC even though they knew ABC.com wasn't available. THEY KNEW IT, so they took ABC.net instead. They could have made you an offer at that time, but maybe they weren't ready because their business wasn't profitable yet. No point in putting money into something isn't proven valuable yet, right? So they kicked that can down the road; delayed that decision to buy your domain.
So, now they want it, and they're engaging you now. They know they have no more claim on it than they did 2 years go.