The Yankees had a tremendous month in June. Any team who can bring together a 22-6 record in a calendar month are going to be out there in the lead and the Yankees expanded their lead in their division from 5.5 to 12.5. A truly impressive series of performances.
Also, to this point in the season the Yankees are managing to remain injury free. They have had relatively few new injuries and some of their long time unavailable players are working their way back.