The problem is both quality, consistency and lack of rivalries.
It becomes quite clear when Fedal doesnt play, there really are no rivalries. If you take away Djokovic, who is the favourite?? I mean, you really have 20-30 players that could win without Djokovic, i wouldnt have the slightest idea who to pick for second favourite in this field. Among the players from 20 to 32 years of age, you dont have a single rivalry. They might win a tournament, then lose R1 the next two tourneys. There is absolutely no consistency. Until recently, the biggest opponents of the Big3 was the second layer of their own generation. Now there are more young players in the final stages, but i fear its more because the older guard have retired/declined, more than the younger players stepping up.
As a Norwegian i enjoy young Casper reaching R3, but he still has a looong way to go... If he ever gets there...