Thankfully, he also answers the question, with a bit of background information: Briscoe, thechineseroom's Dan Pinchbeck and Jessica Curry, and coder Jack Morgan made the 2012 PC launch game, and then the team split to work on their own things (Amnesia, anyone?). Briscoe outsourced the Mac and Linux ports of Dear Esther to two separate teams, which have since dissolved and stopped bug-fixing those versions. Another, native Linux port, is still in beta and looks like it's staying that way.
Briscoe received a "huge bill" for the middleware included in Source Engine but not covered in the original licensing deal. The team wasn't aware of the middleware or its fees before getting the bill, and it had to pay for a separate license for each platform. "It was a big hit financially, which put us at a loss in terms of the Mac and Linux ports," Briscoe says.
The PS3 port, started in May 2013 and expected to take three months, caused problems from early on. First, Briscoe had to license more middleware for Source and get the PS3 source code.
"This was all happening around the time of the departures at Valve, which unfortunately included our main contact for all things Engine related, and subsequently we spent weeks trying to find someone else who could point us in the right direction," he says. "This had a cascade effect on the whole project, leading to months of delays; coupled with the contractor's inexperience with the engine, communication problems, and then finally the PS4 release date announcement, we decided it was time to pull the plug, at significant cost to us.
"We also got the underlying impression that official engine support was not long for this world, making me all the more anxious, not just about the possibility of further ports, but about the future of Dear Esther in the years to come."
Briscoe had tinkered in Unity previously, and when he discovered the Playmaker and Shader Forge plugins, he felt comfortable making the leap.
"When the PS3 port collapsed, I realised that with my knowledge of Unity, there was an opportunity to not only safeguard the future of Dear Esther, but to also clean up the Linux and Mac ports, and reach a wider range of other platforms," he says. "Best of all, we'd be able to keep everything in-house, at low cost, with no more licensing or communication barriers, no more support woes and no more scouring for experienced Source Engine developers to help us."
Briscoe is working on the Mac and Linux versions first, and then he'll tackle PC. He plans to launch betas for Humble Bundle and Humble Store customers to test out before full releases. For technical minds, Brisoce has posted a "How?" blog detailing the Unity transition.