If Knight promotes at 5c, the value of the piece will increase by 2 points. Since Gote did not lose any piece, the point gap created is also 2 points.
However, if you do not promote, then the Knight is now forking Golds
Knight take a Gold.
and finally, Gold pick up the Knight. This exchange is +6-4=2 points. Again there are 4 points gap created among players with this exchange. Also note that Sente still has a turn. So in this case, not promoting Knight was a good decision.