They must have figured the income from the game would not have even covered costs of manufacturing, so it actually lost them less money to not even bother to publish it.
Plus if you recall the DC port had multiplayer stripped out in favor of a later disc with multiplayer only. Perhaps they feared that if they never delivered the second disc people would cry foul. When Mattel marketed the Intellivision system as having a future keyboard "so it could be a computer" and then backed out of the keyboard idea the customers sued them, saying that waiting for the keyboard was the reason they bought the thing in the first place. Mattel was forced to make the thing available and as predicted, it didn't sell and they lost even more money.
Sure, Sierra could just not advertise the game as such but the fact that the #1 reason people like Half-Life
(the multiplayer modes - I think the plan was the second disc would have TF2 and such) couldn't be included was one more factor against the port.