The reason they didn't score on first and goal all have to do with them not being good enough. Henderson couldn't outrun a safety coming across the field from the other sideline, Higbee got thrown into the backfield by a linebacker, and Everett got pushed back by a guy he outweighs by 42 pounds. The Seahawks said to a man after the game that they simply were not going to let the Rams into the end zone down there. They just refused to entertain even the idea of the Rams getting into the end zone.
Yes, Goff did throw an interception; imagine a quarterback doing that. If our defenders could make plays in big games, we could have started the game with a pick six!
Why focus on just the quarterback's mistakes?
The Rams were not going to get into the end zone down there. Not in any form. The Seahawks had willed that scenario out of existence.