They rebuilt a game in Unreal 4.
So yeah from the ps1 era almost everything had to be redone from scratch. I fail to see the problem here. Did player expected them to package the optimized lisp virtual machine they had back then in UE4?
Well, yeah? It's a remaster, not a remake. A remaster implies taking an existing project and updating it. And it makes sense to keep the old game logic - why write from scratch if you already have the whole game in a working state?
N. Sane was done in Alchemy Engine, not Unreal Engine 4 (unlike Reignited), although VV is likely following suit with their upcoming project.