tomimt: To continue selling it, they would need to patch out now disabled server authentications. It doesn't only prevent the use of bought DLC, it also prevents the players from moving to chapter 2. Now, people can advance in-game, if they are willing to modify the game files, but let's face it: if you buy a game, you should not have to do anything of the sort. Pulling the game from Steam was the easiest and the cheapest option for Ubi.
Quickly checking, at least there appears to be an "abandonware" version of the game online, so I presume someone have already fixed the issue of not being able to move beyond chapter 2 and whatever issues there may be.
The problem is at least I am reluctant to try out modified versions by Russian and North Korean hackers, not knowing what exactly they have modified (malware warning), even if I didn't have any moral objections to use such a version. But I guess Ubisoft could contact those sea pirates to use their cracked version for a repackaged DRM-free version. I don't think it is unheard of that old classics have been re-published and sold using some existing cracks...