And why wouldn't they keep it? It's what makes Mass Effect, Mass Effect!! Without paragon or renegade you take away the critical choices and possible multiple endings and opportunities for a branching storyline.
Dropping Paragon and Renegade designations doesn't stop you from having a story with choices and branches. You could even still write the scenarios to be similar to what Paragon and Renegade were supposed to be with idealism vs. pragmatism and expediency (hopefully they would make the outcomes more balanced this time).
The problem is that a binary morality meter feels dated and simplistic, choices don't always fit within its confines, and while they significantly improved how Renegade was written in ME3 the well was still poisoned from how poorly it was often handled in the first two games.