It is incredibly difficult to gain entry in to a Diamond League race. INCREDIBLY HARD. You have no idea. It is also isn't a walk in the park to make a US Olympic or World Championship team.
That said, they all ran 3:55 miles and swept it (a prestigious mile event in Europe) in dominant fashion. Also, might I add, 5 days after doing something similar in Italy and having traveled across Europe.
That is impressive if you ask me. Even if you take the time out of it, which is fast in of itself, how often do you see training groups do this? It makes the sport fun for them and American fans.