Because they are a models company and not a game company. It's not like they are called GAMES workshop or anything.
But also because it's a simple matter of resources - they don't want to divert resources to things that aren't selling. "But those things aren't selling because they haven't updated the rules." yeah, funny how that works! Besides why should we support them anyways. they are just a company going for a money grab. We should just order the cheap knock-offs from 3rd party Chinese sites cause they are cheaper. It's not like it hurts anyone or damages the hobby, right?!