Mate, it's perfectly normal to call it quit at some point. You can't just provide updates forever... Otherwise we wouldn't ever get new games.
Yes, there's still communities on Doom 2, Unreal Tournament, Age of Empires 2, Starcraft Brood War... Yet we didn't see **** for YEARS. And it's perfectly normal. Once the story has been wrapped up, once we've done everything we wanted on a game... we just need to move on. If not for economic reasons, at least on a purely artistic way.
And...Well duh? Yes they are suggesting you to move to KF2 because that's where everything happens now? I mean, that's what sequels are for. To improve on a formula, to go beyond. Nobody is forcing you to do so, but you have to understand that not only Tripwire but people in general have moved on to other things. That's how you progress.
Tinker with mods if you want some extra fun. But you can't scold Tripwire for not caring about an 11 years old game.