The apparent discrepancy can be attributed to a sharp reduction in the fee Goldman earned as a proportion of the M&A Deal Value
The primary reason for lower fees per deal is intense competition among M&A players during a period that has seen a sizable reduction in new M&A deals.
Also, deals greater than $10 billion in value increased 21% y-o-y. As large deals have several investment banks working together, the fees are also distributed among the various banks involved.
Finally, as playing a less prominent role in a large deal would mean a smaller share of the fees earmarked for the deal, Goldman very likely also had a supporting role in many of the largest deals that closed over the period.