Why did early resolution of the murder damage the quality of season 2, when the murder was never the main focus in the first place?

So I heard ABC executives forced the showrunners to resolve the murder earlier than they planned. The show's quality declined after that.

However, from what I can tell, the majority of the show was not about investigating the murder anyway. So why would resolving the murder be such a big deal? Was season 2 originally supposed to be focusing on the murder investigation, or a large chunk of plot depending on it?