I mean I like the idea of Cataclysm on Steam for one reason;
Achievements.
But I highly doubt it’d ever be done, maybe not even possible at all. That said, even if it were possible, what would they do? Upload the latest stable version to Steam? The latest stable version was released two years ago, and lacks a great deal of things that were implemented in to the experimental versions which we all know and love.
They could just put one of the latest experimental versions up there then, but considering a new experimental version is released multiple times daily, the game would never stop needing to be re-downloaded/updated.
Not to mention the obvious fact that the experimental versions like to bitch slap you with a crash at the best of times, throwing Steam in to the mix would just make things worse.
Better to avoid all that and stay snuggled up where we’re all cosy and warm, away from Steam and everyone else, remaining in our own little apocalyptic world. 