Firstly, you don't find 'more realistic' in my statement. So you are fighting with ghosts that live in your head, mate.
But why IZ2 is more fantasy compared to NP is not when compared to realism, but to sci-fi. In IZ2 you can be a two legged a rhino or tiger - it totally breaks the genre for me. I think this design choice was made to compete with the success of Shadowrun.
The Hybrids weren't put in to compete with Shadowrun, they were put in because the creator of the game "Dave Jarvis" came up with the idea and thought they were cool.
This became a point of contention to a small degree, as I was more in favor of far more subtle Hybrids where a portion of the fan base and Dave Jarvis himself liked the full on TMNT style mutant Hybrids.
I left Gun Metal Games not entirely on the best of terms. I'm happy with it's success to a great degree, but there were several design choices I was against, and or in favor of something else. Ultimately this is why I parted ways with the company when work on the IZ 2.0 book was completed.
An example of this being the inclusion of the "Bioroid" race and the "Simulacrum" race...
To me, Bioroids are literally just Simulacra by a different name. They're both artificial people grown in a vat for a specific service...But one of the writers really didn't like the idea that Roy Batty and the Puma Sisters are the exact same thing just different presentations.... So that's how we got the "Bioroid" race for Japan.
I still am very proud of the work done on IZ 2.0, it's a beautiful book, and it has some of the best rules and writing in RPG's, design wise thought, I would have tweaked a few things differently.