That 2.1 average for all of the telecasts included the women's finals, and women's semis, which were also significantly above the overall average. If you take them out of the mix, the remaining telecasts drop under a 2.0 average.
The funny part about the ratings is the networks getting their comuppance for a decade of jingoism, with NBC being among the most nationalistic. Now, faced with a near future of most grand slam men's finals having no Americans, they are trying to backtrack. It used to be different. Fans used to tune in to watch the likes of Borg, Lendl, Wilander, Edberg, Becker, even if they weren't playing Americans. There might be a slight dropoff in ratings vs a match with Americans, but it wasn't as steep as it is now.
The networks have only themselves to blame, after a decade of sowing "only Americans matter". Reap and weep, baby.