The lack of present day sections in Assassin's Creed: Unity was intentional but it wasn't for artistic reasons.
In fact, lead writer Darby McDevitt wished to have more modern day gameplay before he was faced by technical and logistic limitations.
"We always plan to have more modern day but we have to be really smart about how we do it. There was a plan for a little more modern day in Unity - a plan," he explained. "nothing that was actually cut."
"The thing with Unity was that it was a completely fresh game on a completely fresh generation. So creating any kind of modern day is a pretty huge ask. To create a city, for instance, or even part of a city, would require six months of work by many, many artists, designers, modellers. And then you'd need gameplay systems that didn't feel like you were just fencing."
Going forward, McDevitt and the team plan to have more present day sections in upcoming Assassin's Creed games.