More importantly, why they traded away all those picks to get Goff.
1. Fisher/Snead needed a lifeline and they're hoping Goff is it. They won't be around to suffer the consequences of that deal if he's not, so they had nothing to lose doing it.
2. Kroenke wanted to make a splash going into LA and knew Goff would keep the team in the headlines, generate fan excitement and sell a lot of jerseys in LA for the next year at least. If not for the move to LA, it's doubtful he'd have allowed a front office on thin ice to risk the next several years on a single player.
In other words, they took Goff for the wrong reasons, but he could pay off anyway. Short of a Kurt Warner type miracle finding his way into the system over the next couple years, he better.
