Goff was holding a stacked Rams team back and Stafford came in as a consistent franchise guy and was able to get that team over the hump. For a franchise that was irrelevant since the start of the Pats dynasty and the fact that Stafford's legacy as a player isn't going to change a whole hell of a lot over the next 1-3 years he probably has left, I don't see a single reason why he should do them any favors. Take the money while you have the leverage.
Everyone knew the rams were just selling out for a ring. They got their ring and now they have to pay the piper and they are upset that they have elite talent like Donald and Kupp who are primed right now that might not be by the time they get out of this. It's the price you pay for going all in short term. But it could be worse. Plenty of teams tried to build responsibily and methodically and never got a ring for it.