Back during the Kickstarter, we were clear about the vision, to make a phenomenal new sequel to Elite in an online world, which we believe we are about to deliver. At the time we believed we could also offer a good single player experience, and base an acceptable offline-only experience off that. As development has progressed, it has become clear that this last assumption is not the case. That experience would be empty at best, and even that would take a lot of extra work.
It is not to enforce DRM or advertising as you suggest. We will be judged on quality, and the quality of that game experience would be poor, and we don't want to deliver a poor game. To make a richer offline single player experience has always been possible (and still is) but would be a separate game with its own story content. A huge slice of separate work. We have developed a multi-player game with an unfolding story involving the players, and groups collaborating with specific objectives and taking account of all players behaviour. This is what the game is about. Without this it would not be the rich gaming experience that we will deliver, and would be a great disappointment to all players.
I don't pretend it was an easy decision, but it was done to benefit the game as a whole. One thing we have looked at carefully is our requirements of the network connection. For the single player game they are pretty light. I myself have played the game fine on the train using a laptop on a tethered connection over my phone. Given that this is a game which is only available online, this was the decision we took. I am sorry that people are so upset about it, but it was the right decision.