There could very likely be technical or legal reasons why certain games will never make the jump. In this case, I very much doubt it was just a choice to work on the sequel first, as you seem to imply. They would probably have liked to start with the first game but simply can't.
The first Darkness seems to really be banished to the past, from a lack of PC port after 10 years to a further lack of backwards compatibility to date, besides the fact that if I'm not mistaken it was added alongside The Darkness 2 on PS Now. The name and impact of that game would really grow with a fresh audience that could access it again. The lack of a PC port is really baffling to me, though. Judging by its addition to PS Now where it was accompanied by the entire family of 2K published games, including Spec Ops, that might be a clue into whose hands it is in at present. To me it seems like it's firmly in the grasp of 2K and shouldn't be too much in limbo in terms of rights or licenses, but then again the PS Now fact is my only real basis for thinking that.
There's also the fact that 2K has a precedent in not being been totally consistent in porting console releases to PC like RDR as the biggest example, and that could also be the reason The Darkness hasn't been ported to PC yet while The Darkness 2 has.
Next up, bring on...to name a few
Blur
Ace Combat 6
Amped 3
Ninja Gaiden 3
Lollipop Chainsaw
Rez
Mark of the Ninja