Torment: Tides of Numenera - Interview @ Colony of Gamers
Here's their explanation on why they returned to the Torment universe - to make a game:
CoG - What was the impetus behind trying to get this project done next, instead of say more Wasteland 2? Why the return to Torment?
Kevin - Planescape: Torment was a game that Brian was very proud of from Interplay, in that it was a risky game for him to give the go ahead. Though it wasn't considered a fiscal success, it had a strong following. That's the market we're in with crowd funding. The market that's very passionate about their games. Here's a game we know that people really care about. As much as people talk about Planescape, there hasn't been a game that tied directly to it in terms of gameplay in all of these years....
Colin - That was certainly my hope. Chris Avellone and I had been talking about making our own Torment title. We didn't get very far. A few months later we found out that Brian had purchased the Torment IP. When he brought the idea up to me, I checked with Chris and asked him want he wanted to do. Chris said that he couldn't do it right now, but that he wanted to give it his blessing. This is a game I've been wanting to make for years. The time is right because there is a perspective of years that has changed the nature of the question we want to ask.
Source: RPG Codex