https://en.wikipedia.org/wiki/Consumer_welfare_standard
Maybe the judges are confused, but there was a shift in enforcement around the Reagan era. I also think "consumer welfare" in this context is taken to mainly maen low pricing. That is, if a monopoly causes higher prices, then we should go after them. The DOJ going after Google and Amazon is a bit of a return to the former standard. (Source: news programs I listen to such as The Majority Report.)